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Modelling rhetorical legal “logic”—a double syllogism
Int. J. Human-Computer Studies (1999) 51, 1173}1188 Article No. ijhc.1999.0299 Available online at http://www.idealibrary.com on
Modelling rhetorical legal ‘‘logic’’ca double syllogism JOHN S. EDWARDS AND ROBERT I. AKROYD Aston Business School, Aston University, Aston Triangle, Birmingham, B4 7ET, UK. email: [email protected]
This paper looks at legal reasoning from the point of view of the work of the lawyer, rather than the law itself. In the case of Common Law systems, this means a more #exible view of how tasks are divided between the humans and the computer system, with an emphasis on decision support rather than complete automation. A process-based model of the lawyer's work is proposed in the form of a double syllogism, which displays an aesthetically pleasing symmetry, but also a signi"cant asymmetry in the role played by perceived precedents. This arises from the use of inductive, rather than deductive, reasoning. The potential complications arising from the issue of the perception of precedents are discussed in depth. The double-syllogism model is then considered in the light of CommonKADS terminology and models. It is suggested that decision support systems using knowledge-based techniques, as required to support lawyers working under Common Law jurisdiction, raise a stronger form of the interaction problem that is well known in knowledge-based systems. This means that such systems are not well catered for in the existing CommonKADS Organisational, Agent, Task and Communication Models. The double-syllogism model is suggested as a supplement to CommonKADS in the development of such systems, at least until a more generic addition is available. ( 1999 Academic Press
1. Introduction This paper takes a di!erent perspective to that of the majority of arti"cial intelligence (AI) based work on legal reasoning, in that its focus is on the lawyer rather than the law itself. Although lawyers and the law are of course inextricably linked, this di!erence in focus, it will be argued, leads to a di!erent view of the computer support needed, and thus the knowledge modelling required. This helps to put into perspective the work that has been done so far, and what more is required. AI work focused on the law has tended to concentrate on the written elements of statute and case, or on relatively well-de"ned procedures such as sentencing; see for example Capper and Susskind (1998) and Bainbridge (1991). Statutes or sentencing guidelines may change over time, but the systems treat them as "xed; their content is much more important than the process of which they form part. Although there may be process aspects involved, there is a tendency to concentrate on reasoning in a static situation, such as: (1) does this statute apply in/to this case? (2) what is a reasonable sentence in this case? By contrast, when the focus is on the lawyer, especially in a Common Law system such as that of England and Wales, the process of working with the law becomes more 1071-5819/99/121173#16 $30.00/0
( 1999 Academic Press
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important in terms of achieving the desired outcome(s) than the content of the law itself. This is essentially a dynamic situation, not a static one, for two reasons. The "rst is the negotiation aspect that is central to the lawyer's work, especially in commercial law domains. Legal reasoning is still involved, but reasoning about what to do with (or indeed within) the law is now at least as important as reasoning about the law itself. As such, the models that are required must represent process as well as content. This makes them fundamentally di!erent from much existing AI work. Unfortunately, this task of reasoning from a dynamic knowledge base is not one that current AI systems are typically very good at. Accordingly, the models of this type to be described in this paper di!er from those of more &&typical'' legal AI systems. They have more in common with AI planning systems than the deductive assessment systems more often seen in legal domains. A second important di!erence is the way in which the models are to be used. The authors believe that in process-based work such as that of the lawyer, the role of the model must be to provide decision support, not to make the decision. This is because, in principle, every legal case or &&matter'' is di!erent, especially in a Common Law system, and the lawyer must make strategic decisions in this light. To borrow a phrase originally intended to describe management, lawyers operate in &&a world in which nothing ever happens twice'' (Rivett, 1983). Although there is considerable scope for the use of AI techniques in modelling legal knowledge, as will be discussed, the techniques must be subservient to the lawyer's choice of strategy; a choice that may have far-reaching consequences. Previous work has demonstrated that the development of systems from this standpoint is possible; including the prototype legal knowledge-based systems (KBS) SALES CONTRACTOR and CONTRACT NEGOTIATOR (Akroyd & Edwards 1995a, b; Edwards & Akroyd, 1995). The principles of the approach to be described here apply to all Common Law systems, although the paper concentrates speci"cally on that of England and Wales. The structure of the paper is based on a model of &&rhetorical legal logic'', i.e. the lawyer's approach to a case, in the form of a double syllogism. The "rst section makes the case for such a treatment. This is done in some detail, because it is an aspect rarely considered in investigations of legal reasoning, with rare exceptions such as the article by Smith (1996). The overall process model is then presented in three complementary forms, demonstrating both a fundamental symmetry and a signi"cant asymmetry between the two syllogisms. The latter relates to the use of inductive, rather than deductive, reasoning. The argument is also put forward that most existing legal KBS work lies within one of the two syllogisms only. The second section considers the model of the "rst section in the light of the CommonKADS terminology and structure (Schreiber, Wielinga, Akkermans, Van de Velde & de Hoog, 1994). The interaction problem between domain and control knowledge is argued to be at its most severe in Common Law systems. In particular, the strategic knowledge, seen as a crucial element of the problem-solving method in the Expertise Model, is so central to deciding what must be done that it a!ects the task knowledge part of the Expertise Model, and these links may also involve the Task Model, the Organizational Model and the Agent Model. The implications of this for knowledge engineering are discussed, including the cyclical overlap of planning and assessment tasks in a lawyer's work. The use of the models for decision support, rather than fully automating decisions, is seen to be critical in managing this interaction problem.
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In the light of the importance of the strategic choice, and the decision support role of the system, it is therefore clear that most legal reasoning systems must be designed for a specialist user*a lawyer or other fee earner*to use, not for lay people. The view of the authors is that su$cient separation of domain knowledge and task knowledge may be achieved for useful modelling of both process and content to be accomplished, but that a great deal of work still remains to be done.
2. The role of the lawyer The emphasis here, as it will be throughout this paper, is on decision. Lawyers may thus be seen as strategic decision support intermediaries between a captive market population of &&customers'' for legal services and a monopoly sovereign state &&supplier'', providing advice and advocacy in negotiating legitimate relationships and resolving disputes. In doing so, however, the lawyer must attempt to respect both the aspirations of a client to have his/her unique circumstances taken into account and the requirements of the sovereign jurisdiction for a coherent, predictable, normative system, by reconciling the normative paradox between the individuality of experience and the predictability of normative systems. Aristotle de"ned justice as treating all like cases alike, but if there are no like cases, and normative systems treat unlike cases as alike, for the purpose of treating them similarly, then normative systems are inherently unjust. This is not a simple matter of trade o! between the desirable and the achievable. We can note with Oliver Wendell Holmes that: &&The training of lawyers is a training in logic. The process of analogy, discrimination and deduction are those in which they are most at home. The language (our italics) of judicial decision is mainly the language of logic. The logical method and form #atter that longing for certainty and for repose which is in every human mind but certainty generally is illusion and repose is not the destiny of man.'' (Novick, 1995)
However, as has been pointed out elsewhere, the logic referred to here is not the same as either mathematical logic or computational logic (Greinke, 1994). Nor is it the same as deontic logic (Susskind, 1987), despite the amount of consideration that has been given to it in legal reasoning. The phrase &&rhetorical logic'' is suggested, to capture the #avour of the presentation of legal argument. Although they may be seen to specialize in particular "elds, lawyers cannot choose their clients' &&matters''. Nor are English lawyers generally allowed to reject a client whose case may be hard to present successfully, however unpopular or hard pressed that client may be. The process of an adversarial lawyer's work, especially advocacy, is thus more concerned with rhetoric or argument than with the justice or injustice of a cause. The legal decision process is a complex one in which sequential sub-processes shape decision outcomes. In Common Law systems, the doctrine of precedent, which arose out of the customs of the judiciary, is crucial. There are three key elements in the Common Law process of rhetorical logic. f f f
Pleadings*de"ning the issues. Legal authorities*both statute and case law. Evidence of the facts.
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FIGURE 1. The double syllogism*&&logical'' form.
Formally, the sequencing arises from the process of legal &&proof'', which moves from issue to issue within the "elds of law and evidence in dispute, albeit with much iteration and backtracking. These interactions have been described elsewhere (Akroyd and Edwards, 1995a, b). This sequence is modelled in this paper in the form of a double syllogism, as shown in Figure 1. This is a characteristic skill in the marshalling of arguments, which is central to the work of the legal profession in all Common Law systems (Smith, 1996). Each syllogism has two premises. In the "rst syllogism, the "rst premise represents the desired decision outcomes from any disputed issues. The second premise represents legal authorities; the perceived precedents giving rise to the desired outcomes (rather than less desired or undesired ones). The conclusion is a characterization of circumstances within the law of evidence; what evidence of what &&facts'' is needed, or not needed? In the second syllogism, the order is reversed. The "rst premise now represents characterized circumstances within the law of evidence*&&the evidence''; the second premise again represents legal authorities/perceived precedents, giving rise to the conclusion, the desired decision outcomes from any disputed issues. Thus, the "rst part of the process is open-ended and characterized by the word &&because''; an essentially inductive operation. The second is closed-ended and characterized by the word &&therefore''; an essentially deductive operation. In both parts of the process, the law plays a central role, providing a common element with both the "rst premise and the conclusion; in both parts the legal authorities/perceived precedents formally constitute the syllogism. The diagrammatic form in Figure 2 suggests how each premise will in fact be made up of many part conditions; although these will by no means necessarily follow a simple production rule structure, production rules will be used by way of illustration in the remainder of the paper. The &&double-syllogism'' model provides an aesthetically pleasing degree of symmetry, as is emphasized in its third form; the diamond shown in Figure 3. This "gurative representation also avoids specifying the detail too precisely. However, there is also a signi"cant asymmetry between the two syllogisms, in the form of the role played by the precedents in the two parts, which is substantially similar rather than opposite. This is where the double syllogism di!ers from simple backward and forward chaining by deductive inferencing, in the inductive role of the precedents in the "rst syllogism. This will now be explained further.
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FIGURE 2. The double syllogism*expansion into part conditions
These two key sub-processes in syllogistic legal argument can conveniently be labelled: (1) &&tracing the antecedents of the decision'' and (2) &&establishing the consequences for the decision''.
2.1. TRACING THE DECISION'S ANTECEDENTS (SUB-PROCESS A)
This is a research-based exercise. Precedent has not been widely considered in the legal AI or KBS literature. In Common Law systems, it is not simply a question of identifying precedents in the form of relevant cases by using a similarity measure as a case-based reasoning system would. There is a place for such an activity, and there may be scope for using such a system, but the important point lies in the phrase perceived precedent. Tracing the decision's antecedents is capable of heuristic, inductive use, both by the lawyers involved in preparing a case and indeed the judges called upon to give judgement in it. The potential for the heuristic use of precedent arises from the impossibility of an exact match between any two case circumstances, combined with an increasing plethora of potential analogies, as the database of case precedents continues to grow, apparently exponentially. The tendency for heuristics (in the strictest sense of the term, as rules of thumb used by many) about legal principles to arise in opposing/contradictory pairs, as discussed by Smith (1996), provides a further incentive for inductive reasoning. Deductive reasoning with such a rule set would be fruitless.
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FIGURE 3. The double syllogism*"gurative representation.
The inductive heuristic process is subtle. It begins with what situation(s) or remedies the client wants. It then goes on to ask what combination of legal criteria supported by case precedents will give such a desired outcome. The criteria are invoked, if at all, only by admissible and convincing evidence of often subtly distinguished circumstances. The subtlety here is that the proposition inferred is not, as might be imagined, solely one of substantive legal principle, but also of provable situation, a conclusion of evidence speci"c to the particular case. It is the rhetorical characterization of a client's case that is at the root of legal argument. Thus, the process of induction from one precedent to legal and evidentiary principle is a double one. It is based on characterization with hindsight of the supposed reason for a decision (ratio decidendi) on legal and/or evidentiary matters actually in issue. This hindsight is not the simple deduction of backward chaining, "nding sequences of rules that exist. It is a covertly creative activity, equivalent to modifying the rules or "nding
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new ones, to yield the most convincing path to a &&necessary'' decision. This asymmetry makes the double syllogism necessary, and this important distinction has given rise to the creative uncertainties of stare decisis so clearly revealed by the judicial career of Lord Denning, and the essentially adversarial Common Law process of dispute by advocates. Note that, for clarity, the examples that follow are all chosen from the arguments of judges rather than those of lawyers which, although also available in law reports, are presented in an overtly adversarial manner, bringing a further degree of complexity. In Common Law jurisdictions, however, judges are appointed solely from the ranks of lawyers experienced in the same mode of reasoning. In Harper v NCB [1974] 1 QB 614, 618 et seq., Denning MR was faced with the seemingly intractable problem of having to follow an inconvenient binding precedent of the House of Lords. His line of reasoning displays characteristic ingenuity, and evidence of the double syllogism in action: &&We can only accept a line of reasoning which supports the actual decision of the House of Lords. By no possibility can we accept any reasoning which would show the decision itself to be wrong. The second proposition is that if we can discover the reasoning on which the majority based their decision, then we should accept that as binding upon us. The third proposition is that if we can discover the reasoning on which the minority based their decision we should reject it. It must be wrong because it led to a wrong result. The fourth proposition is that, if we cannot discover the reasoning on which the majority based their decision, we are not bound by it. We are free to adopt any reasoning which appears to us correct, so long as it supports the actual decision of the House 22''
Denning's "rst three propositions follow deductive logic through to its limits with the existing rule set. The fourth proposition "nds the existing rule set insu$cient for the task, and invokes an inductive step to devise new rules. Denning continues: &&Applying the propositions to Smith v Central Asbestos Co. Ltd. (Dodd's case), [1973] AC 518, the position stands thus: (1) the actual decision of the House in favour of Dodd must be accepted as correct. We cannot, accept any line of reasoning which would show it to be wrong. We cannot, therefore, accept the reasoning of a minority of two*Lord Simon of Glaisdale and Lord Salmon*on the law. It must be wrong because it led them to the wrong result. (2), we ought to accept the reasoning of the three in the majority if we can discover it. But it is not discoverable. The three were divided. Lord Reid and Lord Morris of Borth-yGest took one view of the law. Lord Pearson took another. We cannot say that Lord Reid and Lord Morris of Borth-y-Gest were correct: because we know that their reasoning was in con#ict with the reasoning of the other three. We cannot say that Lord Pearson was correct: because we know that the reasoning which he accepted in the law led the other two (Lord Simon of Glaisdale and Lord Salmon) to a wrong conclusion. So we cannot say that any of the three in the majority was correct. (3), the result is that there is no discernible ratio amongst the majority of the House of Lords. In these circumstances I think we are at liberty to adopt the reasoning which appears to us to be correct.''
The manipulation of precedent arises out of situations where either: (1) there is a need to create &&decision space'' within an over-abundance of case law precedents (&&too many rules'') or (2) there is an over-riding need for any &&colourable authority'' (relevant precedent) and the precedents are few and/or weak (&&too few rules''). (1) Where there is an over-abundance of precedents.The key skills in this process stage are the reconciling of apparently con#icting decisions and the distinguishing of apparently similar case situations.
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In fact, these apparently distinct skills are the &&two sides of the coin'' of a single high-level task that includes aspects of both assessment and planning, as will be discussed in more detail later. A major example of the reconciliation of apparently con#icting decisions is Lord Denning's long-running battle to establish that, where the creative construction of evidence &&revealed'' a broken fundamental term in a contract, a rule of law prevented any exclusion of contractual liability. In the Suisse Atlantique Case [1967] 1 AC 361, a conservative House of Lords eventually held unanimously in favour of a more elegant alternative. Accordingly, where evidence of the whole agreement, including any exemption clause, revealed its fundamental breach, it was a matter of fact rather than of law, that the exemption clause was necessarily too narrow to cover the breach. This approach had the additional advantage of including multiple minor, but damaging breaches. However, because exclusion clauses had not been directly in issue in the Suisse Atlantique Case, the judgement could be characterized as merely persuasive (obiter dictum) rather than binding. Hence, in Farnsworth Finance Facilities v Attryde [1970] 2 All ER 708, Denning MR was able to reassert his own doctrine as wholly consistent with the judgement of the House of Lords (sic), for the purpose of preventing an exclusion of liability, where the aggregation of minor defects in a motor cycle had rendered it virtually useless. E!ectively, this is denying the existence of a rule that might appear to some to be in the rule set. An example of a distinction being made between apparently similar case situations is the judgement of the Court of Appeal in Lewis v Averay [1972] 1 QB 198, distinguishing its circumstances from those of its earlier decision in Ingram v Little on the basis of an arguable distinction between identity itself and such attributes of identity as fame, wealth and so on. According to English legal principle, where fraud induces an original owner of property to contract on the basis of mistaken personal identity, the contract will be void, enabling them to reclaim the property. If the mistake was one of personal attributes such as credit worthiness, however, the contract will be voidable only, requiring the original owner to complete some further act of &&avoidance'' before some innocent third party acquires proprietary rights. As Lord Denning says at [1972] 1 QB 206, this is a distinction without a di!erence. The means of checking identity are rarely e!ective or logical. In Ingram v Little [1961] 1 QB 3l, the original owners' act of checking an interim dealer's identity by looking up his (false) name in a telephone directory formed the basis of the Court of Appeal's decision, thereby allowing the original owners to reclaim their car, as being sold under mistaken identity. In the very similar Lewis v Averay [1972] 1 QB 198, the original owners were only persuaded of the interim dealer's identity by checking his (false) name, picture and other details on a forged "lm studio pass, but nevertheless could not reclaim their car as being under a mistake as to attributes only. A rule had been &&invented'' to distinguish the two situations. (2) Where precedents are few or weak. Sometimes, moreover, legal decision shapers are faced with the converse situation where, the most diligent research having failed to reveal any genuinely convincing precedent, the heuristic proceeds on the basis of &&colourable'' (barely acceptable) authorities and/or those of weight but little direct relevance. In Ray5eld v Hands [1960] Ch 1, for example, the then Companies Act contained provision for a company's memorandum and articles, when registered, to bind the
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company and the members, as if they contained covenants to observe all of their provisions on the part of each member. In fact, one private company's articles required any member intending to transfer shares to inform the directors &&who will take the said shares equally between them at fair value''. The directors were also members by virtue of their quali"cation shares. One such member did so inform the directors and, on their refusing to purchase his shares, brought an action for a declaration that they were bound by the article to do so. The plainti!'s case rested on three issues: on the "rst two, Vaisey J. held conventionally in favor of the plainti!. On the third, he concluded: &&On the whole if22the maxim &validate if possible' applies, I think that the plainti! in this action ought to succeed. Not one of the judges in Dean v Prince [1954] Ch 409 showed any sign of shock or surprise at the assumption there made of a contract between directors being formed by the terms of a company's articles.''
That is, of course, true, but that assumption was made on an issue which was never actually raised in Dean v Prince. It could not, therefore, constitute a precedent for Vaisey J.'s proposition. But how else would he have been able to give judgement for the plainti!? Here, conditions and consequences already present separately in the rule set have been joined in a new way to form a new rule. 2.2. ESTABLISHING THE DECISION'S CONSEQUENCES (SUB-PROCESS B)
By working backwards from the widest possible starting point (i.e. the perception of factual evidence) and proceeding apparently inexorably, via the relevant authorities, to a seemingly inevitable outcome, the open-textured, research-based sub-process A becomes the closed exercise in apparently conventional logic of sub-process B. Sub-process A is often unstated in a legal matter, perhaps even barely conscious, whereas sub-process B is invariably evident. Hence, what initially begins as an open, highly discretionary process is presented as a closed, almost mechanical, process, thereby satisfying both the imperative towards personal sensitivity and that towards normative consistency in judicial decision making. In certain types of situation, this may be signi"cantly varied. In a human rights situation, for instance, where a neo-natural law approach is necessary, sub-process A will be very obvious. On the other hand, in a commercial context, sub-process A will tend to be suppressed in favour of the positivist approach of sub-process B. This is somewhat similar to the well-known &&scru!y/neat'' distinction between pragmatic and doctrinal thought in AI usually "rst credited to Roger Schank. However, there is one crucial di!erence; as stated above, the two sub-processes are not &&either/or'' aternatives. Both sub-processes exist in all legal &&matters'', even though sometimes one dominates the other. Some approaches, for example those just described, "t more closely to one sub-process or the other, and this is mirrored in much existing legal reasoning work. It is scarcely surprising that legal KBSs have tended to concentrate on sub-process B. Fortunately, however, the American realist approach for example, is amenable to both sub-processes (Smith, 1996). 2.2.1. Process support Figure 4 shows the diamond of Figure 3 with the additional adversarial component incorporated, although it should be noted that the overlap of the two diamonds is by no
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FIGURE 4. The double double syllogism (sic)*the plainti! and the defendant.
means necessarily largest near the boundary between sub-process A and subprocess B, as it appears to be in the "gure. Indeed, key skills of the Common Law advocate's rhetoric include justifying their own desired rule set for sub-process B, and anticipating the possible rules set that their adversary might have produced in subprocess A! More detailed process modelling of the three key elements (pleadings, legal authorities and evidence) is beyond the scope of our discussion here. Much of it does not require knowledge engineering in the narrow sense, in that the computer support required is best provided by conventional, rather than knowledge-based systems. For example, the most useful tool in the presentation of pleadings is likely to be a good word processing package, and the speed of e-mail or EDI systems may be highly bene"cial in the transfer of documents or evidence, as long as such systems are admissible!
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3. A CommonKADS perspective on the double-syllogism model CommonKADS (Schreiber et al., 1994; Van Heijst, Schreiber & Weilinga, 1997) has become the de facto European standard approach to knowledge engineering. Its predecessor KADS has been used in the legal domain (Breuker, 1993) to develop an architecture for legal reasoning, TRACS. The TRACS architecture, described further in den Haan (1993, 1996) is designed to support the drafting of legislation. It distinguishes between reasoning about a case and reasoning about legal consequences, by a separate representation of world knowledge and normative knowledge. This mirrors the symmetry of the double-syllogism model to a certain extent, but does not speci"cally include the role of perceived precedents as it is intended for a Civil Law system, the &&legal world'' being modelled essentially as &®ulations''. For example, den Haan (1996) uses TRACS to evaluate the Dutch Tra$c Regulation RVV1990. Breuker (1993) asserts that most legal reasoning tasks fall under the heading of assessment tasks, thus demonstrating the value of the TRACS architecture, since it &&maps easily onto the KADS conceptual model of the assessment''. However, it is proposed here that, at least in Common Law systems, this is too narrow a view of what legal reasoning entails, as will be explained below. Interestingly, den Haan (1996) proposes the extension of TRACS so that it could be used in drafting legislation, a task which would have a closer similarity to the double syllogism. The whole philosophy of CommonKADS is one of knowledge modelling, as opposed to earlier approaches to developing knowledge-based systems, whose paradigm was often closer to that of extracting knowledge from the human expert(s), with all the pain that term implies. CommonKADS comprises a suite of no fewer than six types of model. f f f f f f
Organisational model. Task model. Agent model. Expertise model. Communication model. Design model.
CommonKADS also speci"es the nature of the linkages between these six types of model. In general, all six types of model will be present in any use of CommonKADS, although it is perhaps fair to say that the Expertise and Communication Models are the most developed. The question for knowledge engineers is whether this decomposition is appropriate, or at least adequate, for knowledge modelling in a particular domain. This will now be examined in the light of the proposed double-syllogism model, and the decision support role of the system. 3.1. THE INTERACTION PROBLEM IN COMMON LAW DOMAINS
A central problem in knowledge-based systems relevant to any kind of decomposition has been the extent to which domain knowledge can be separated from control or task knowledge. This separation was claimed as one of the advantages of early rule-based
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expert systems and the expert systems shells that followed. However, it was seldom if ever achieved in practice, and this led Bylander and Chandrasekaran (1988) to state that a complete separation could not be achieved; the so-called interaction problem. KADS originally attempted to achieve this complete separation, but CommonKADS now incorporates a relative interaction hypothesis*that di!erent types of knowledge di!er in the degree to which they are dependent on the task. The domain knowledge may therefore be thought of as a layered set of ontologies or metamodels, each layer comprising knowledge with the same degree of task dependence. The six types of model, together with the relative interaction hypothesis, give a very rich structure for representing not only knowledge, but the organizational context in which the KBS is to be used. Knowledge engineering thus takes on the wider sense of the complete design and development of the system, not just &&putting the expertise in'' any knowledge-based components. However, there are two aspects in which CommonKADS does not yet appear to be su$ciently developed to model the domain of the lawyer's work completely: f f
Level of task de"nition. Modelling of domain knowledge.
Tasks in CommonKADS, as in its predecessor KADS, form a hierarchy of tasks and sub-tasks, in order that a &÷ and conquer'' approach may be taken (Harris-Jones, 1995). The lowest-level tasks, the primitives, typically correspond to the inference functions in the expertise model; tasks such as &&select'' and &&compare''. These are then combined hierarchically to make up the overall task of the KBS. In addition to task and domain knowledge, the expertise model contains problem-solving methods and strategic knowledge. The problem-solving method prescribes how the task de"nition is mapped onto the task body, i.e. how the task is to be carried out. A library of problem-solving methods exists (Breuker & van de Velde, 1994), covering nine problem types including assessment, diagnosis and planning. In principle, the strategic knowledge allows integration of the problem-solving methods as an explicit part of the expertise model, to allow the KBS to decompose the task dynamically. However, the task that a lawyer in a Common Law system might wish a KBS to perform is, it is argued, not so easily speci"ed. The CommonKADS structure posits that the organizational model is used to help identify the top-level tasks in the domain as a whole (which form the task model) and so identify appropriate agent roles for one or more KBSs, with an agent model for each. This assumes that the nature of the links between the organizational, agent and task models is "xed for any given context in which a KBS is used. For the lawyer in a Common Law system, this assumption appears invalid; the #exibility that exists in a Common Law system is such that the very links between tasks, agents and organizational model are not "xed; they are dynamic. Although the communication model allows for a range of interactions between the KBS and other agents, including a human user, these too need to be "xed for a given context. It is notable that Van Heijst et al. (1997) e!ectively begin knowledge modelling with the generic tasks and problem-solving methods. Consider, for example, selecting precedents meeting certain criteria from a precedents database. This is certainly a knowledge-based reasoning task, and so suitable in principle for a KBS. However, it is extremely di$cult to formulate the properties and concepts
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that would be needed to frame the criteria for selection. It is straightforward to conceive that such a list would need to include measures of the similarity of the perceived outcomes, principles and &&facts'' cases to those (desired) in the present case. However, in a Common Law system, it is also likely to be necessary to consider the seniority of the court, the weighting of judgements where applicable (such as 5-0, 4-1 or 3-2) and the personal composition of the court. (These may be thought of as forming an axis orthogonal to the "rst one.) Further, it may also be necessary to select according to elements of the sequence of the pleadings, where such information is available; another aspect of process rather than content. Thus, although the selection of precedents has similarities with an assessment or categorization task, it is not a simple case of such a task, or another task type such as a planning task. It combines assessment and planning, and perhaps diagnosis and other task types as well. The examples earlier in this paper illustrate the complex nature of what is perceived to be a relevant precedent. The relationship between assessment and planning, for example, in any particular selection task will depend on the strategic choices made by the lawyer. Yet these choices may themselves depend on the results of the task of selecting precedents, in an iterative manner. Although CommonKADS allows for recursion in the task hierarchy, it does not yet appear to encompass this high-level iteration, where the nature of the agent's task may depend on the results which that task has already produced, and the communication required may also change accordingly. The relative interaction hypothesis applies at the level of the tasks within the expertise model, not to the interaction between domain knowledge and the overall task that the KBS agent is to perform. In Common Law legal systems at least, there does seem to be such an interaction. Support for this view comes from the work of Kingston (1995). He found, in attempting to apply KADS to the use of KADS, that &&the de"nition of concepts and properties in a domain appears to be context dependent'', so that there is more than one &&correct'' model of any chosen domain. We would expect this to be the case with a Common Law system. Were it not so, then the choice of precedent would be a simple exercise in data retrieval, and there would be no room for the American realist school of thought that &&the judges make the law''. Almost every educated lay person in England over a certain age remembers the case of the drink-driving charge that failed because the police o$cer administering the test was not wearing his hat at the time. It seems an impossible task to construct appropriate problem-solving methods for the expertise model that would take such features into account routinely without guidance from the user. A decision support approach is thus needed, and it is argued that the CommonKADS model structure assuming a "xed task and role for the KBS agent is not capable of capturing this adequately, despite the range of interactions allowed for in the communication model. In a knowledge-based system providing decision support, as with all decision support systems, the relationship between the user and the system is #exible, even beyond the point of division of tasks between them; see for example Silver (1991). At the highest level, the double-syllogism model presented here is o!ering a di!erent perspective on the task, organizational and agent models of CommonKADS. Although the organizational model does include process aspects, as well as functions, it appears that it does not fully embrace the process focus of organizations in the way seen in total quality management (e.g. Oakland, 1989) or business process re-engineering (Davenport,
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1993). The processes in the CommonKADS organizational model seems to be subservient to the functions. Whilst perhaps typical of most legal services "rms until at least the 1980's, this is no longer appropriate as we approach the millennium; the authors have discussed process reengineering in legal services "rms elsewhere (Akroyd & Edwards, 1997). The rigidity that results from this function-driven perspective is limiting the usefulness of CommonKADS in developing knowledge-based components of decision support systems. In Common Law systems, a decision support approach to KBS use would seem to be essential.
4. Significance for knowledge engineering Greinke (1994) shares the conviction advanced here that the provision of decision support is a more fruitful approach to assisting lawyers than that of fully automating legal reasoning. There appears to be plenty of scope, however, for appropriate use of both; using automated, model-based legal reasoning in providing decision support. As conceived here, the whole project of developing such a system is still knowledge engineering, because the knowledge-based elements are central to the performance of the human}system &&team'' as a whole. However, the resulting system must incorporate #exibility at a very high level. It is this #exibility that CommonKADS does not appear to be able to incorporate at present. We would not claim a detailed enough knowledge of CommonKADS to be able to specify a generic form of the necessary changes yet, but in the domain of Common Law jurisdictions, we believe that the more process-focused double-syllogism model, supplementing the CommonKADS model set, will form a suitable basis for knowledge engineering.
5. Conclusion Modelling legal reasoning, and the knowledge engineering that goes with it, is often seen as essentially a task that requires development of either an inductive or deductive system, to achieve a high degree of automation of the reasoning process. The argument that has been presented here is that, at least in Common Law systems, this &&either/or'' approach is too narrow when considered from the perspective of what lawyers do. Each case or matter requires both inductive and deductive reasoning, in the context of a strategy that is developed for that case only. The appropriate mode of operation of a legal knowledgebased system is thus as a decision support system to assist the lawyer (or other fee earner). This support needs to be provided within the context of an overall model of the process in the form of a double syllogism, as has been presented in the paper. This model serves not only as a basis for legal knowledge engineering, but also to indicate where existing work "ts in. CommonKADS is seen as meeting many of the needs of legal knowledge engineers, but needing to be supplemented in designing systems to function in a decision support role. However, the overall construction of such systems is no small undertaking, being at least one level higher than most existing work. Our cumulative work on this is continuing (Akroyd & Edwards, 1995b). To, conclude, it is by no means the authors' hypothesis that the inductive/heuristic and deductive/didactic double syllogism is applicable only to systems of Common Law. On
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the contrary, it is precisely because of its general applicability within the discourse of many disciplines that the signi"cance of its adaptation by legal systems rests. Whilst at "rst sight the double syllogism seems unsuited to the academic inquisitorial culture of the Civil Law process, the deductive/didactic second syllogism is very evident. It may be, moreover, that an inductive/heuristic syllogism might be discernible implicitly at the highly generalized societal level of the drafting of the codes themselves. This might help to overcome the di$culties that Breuker (1993) identi"ed regarding modelling the social system to which and in which a set of legal regulations was intended to apply. Taken to its logical conclusion, this would imply that more complete knowledge-based systems may be feasible in Civil Law systems than in Common Law ones, although this claim is by no means proven yet.
References AKROYD, R. I. & EDWARDS, J. S. (1995a). Computer-supported contract drafting: SALES CONTRACTOR*an experimental prototype. ¹he New Review of Applied Expert Systems, 1, 65}79. AKROYD, R. I. & EDWARDS, J. S. (1995b). Computer supported contract negotiation: CONTRACT NEGOTIATOR * an experimental prototype. In J. C. HAGE, T. J. M. BENCH-CAPON, M. J. COHEN & H. J. VAN DEN HERIK, Eds. ¸egal Knowledge Based Systems: ¹elecommunication And AI & ¸aw, pp. 65}74. Lelystad, Netherlands: Koninklijke Vermande BV. AKROYD, R. I. & EDWARDS, J. S. (1997). Strategic process re-engineering in legal service management. Presented at BAM97, the British Academy of Management Annual Conference, London, September 8}10, 1997. BAINBRIDGE, D. I. (1991). A computer system to assist with the sentencing of convicted o!enders. International Journal of Public Administration, 14, 161}181. BREUKER, J. (1993). Modelling arti"cial legal reasoning. In G. BOY, N. AUSSENAC, B. GAINES & J. BOOSE, Eds. Proceedings of the European =orkshop on Knowledge Acquisition, pp. 34}45. Berlin: Springer-Verlag. BREUKER, J. & VAN DEN VELDE, W. (1994). ¹he CommonKADS ¸ibrary: Reusable Components for Arti,cial Problem Solving. Amsterdam: IOS Press. BYLANDER, T. & CHANDRASEKARAN, B. (1988). Generic tasks in knowledge-based reasoning: the right level of abstraction for knowledge acquisition. In B. R. GAINES & J. H. BOOSE, Eds. Knowledge Acquisition for Knowledge Based Systems, Vol. 1, pp. 65}77. London: Academic Press. CAPPER, P. & SUSSKIND, R. E. (1988). ¸atent Damage ¸aw: ¹he Expert System. London: Butterworths. DAVENPORT, T. H. (1993). Process Innovation: Reengineering =ork through Information ¹echnology. Boston, MA: Harvard Business School Press. EDWARDS, J. S. & AKROYD, R. I. (1995). Using information technology to help business students learn about contract law. Alt-J, 3, 103}109. GREINKE, A. (1994). Legal expert systems: a humanistic critique of mechanistic legal inference. E ¸aw, (Available at URL: http://cleo.murdoch.edu.au/asu/edtech/cleo}web/mdomo/elawj.arcs/greinke.txt). DEN HAAN, N. (1993). Towards support tools for drafting legislation. In J. S. SVENSSON, J. G. J. WASSINK & B. VAN BUGGENHOUT, Eds. ¸egal Knowledge Based Systems J;RIX 93: Intelligent ¹ools for Drafting ¸egislation, Computer-Supported Comparison of ¸aw, pp. 23}30. Lelystad, Netherlands: Koninklijke Vermande BV. DEN HAAN, N. (1996). Automated legal reasoning. Ph.D. Thesis, University of Amsterdam. HARRIS-JONES, C. (1995). Knowledge Based Systems Methods: A Practitioner1s Guide. London: Prentice-Hall.
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KINGSTON, J. K. C. (1995). Applying KADS to KADS * knowledge-based guidance for knowledge engineering. Expert Systems, 12, 15}26. NOVICK, S. H., Ed. (1995). ¹he Collected =orks of Justice Holmes: Complete Public =ritings and Selected Judicial Opinions of Oliver =endell Holmes. Chicago: University of Chicago Press. OAKLAND, J. S. (1989). ¹otal Quality Management. Oxford: Heinemann Professional. RIVETT, B. H. P. (1983). A world in which nothing ever happens twice. Journal of the Operational Research Society, 34, 677}683. SCHREIBER, A. TH., WIELINGA, B. J., AKKERMANS, J. M., VAN DE VELDE, W. & DE HOOG, R. (1994). CommonKADS: a comprehensive methodology for KBS development. IEEE Expert, 9, 28}37. SILVER, M. S. (1991). Systems that Support Decision Making: Description and Analysis. Chichester: John Wiley & Sons. SMITH, J. C. (1996). An introduction to arti,cial intelligence and law: or, can machines be made to think like lawyers? Working Paper, Faculty of Law, University of British Columbia. (Available at URL:http://www.#air.law.ubc.ca/jcsmith/logos/noos/machine.html.) SUSSKIND, R. E. (1987). Expert Systems in ¸aw: A Jurisprudential Inquiry. Oxford: Clarendon Press. VAN HEIJST, G., SCHREIBER, A. TH. & WEILINGA, B. J. (1997). Using explicit ontologies in KBS development. International Journal of Human-Computer Studies, 46, 183}292.
Modelling rhetorical legal ‘‘logic’’ca double syllogism JOHN S. EDWARDS AND ROBERT I. AKROYD Aston Business School, Aston University, Aston Triangle, Birmingham, B4 7ET, UK. email: [email protected]
This paper looks at legal reasoning from the point of view of the work of the lawyer, rather than the law itself. In the case of Common Law systems, this means a more #exible view of how tasks are divided between the humans and the computer system, with an emphasis on decision support rather than complete automation. A process-based model of the lawyer's work is proposed in the form of a double syllogism, which displays an aesthetically pleasing symmetry, but also a signi"cant asymmetry in the role played by perceived precedents. This arises from the use of inductive, rather than deductive, reasoning. The potential complications arising from the issue of the perception of precedents are discussed in depth. The double-syllogism model is then considered in the light of CommonKADS terminology and models. It is suggested that decision support systems using knowledge-based techniques, as required to support lawyers working under Common Law jurisdiction, raise a stronger form of the interaction problem that is well known in knowledge-based systems. This means that such systems are not well catered for in the existing CommonKADS Organisational, Agent, Task and Communication Models. The double-syllogism model is suggested as a supplement to CommonKADS in the development of such systems, at least until a more generic addition is available. ( 1999 Academic Press
1. Introduction This paper takes a di!erent perspective to that of the majority of arti"cial intelligence (AI) based work on legal reasoning, in that its focus is on the lawyer rather than the law itself. Although lawyers and the law are of course inextricably linked, this di!erence in focus, it will be argued, leads to a di!erent view of the computer support needed, and thus the knowledge modelling required. This helps to put into perspective the work that has been done so far, and what more is required. AI work focused on the law has tended to concentrate on the written elements of statute and case, or on relatively well-de"ned procedures such as sentencing; see for example Capper and Susskind (1998) and Bainbridge (1991). Statutes or sentencing guidelines may change over time, but the systems treat them as "xed; their content is much more important than the process of which they form part. Although there may be process aspects involved, there is a tendency to concentrate on reasoning in a static situation, such as: (1) does this statute apply in/to this case? (2) what is a reasonable sentence in this case? By contrast, when the focus is on the lawyer, especially in a Common Law system such as that of England and Wales, the process of working with the law becomes more 1071-5819/99/121173#16 $30.00/0
( 1999 Academic Press
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important in terms of achieving the desired outcome(s) than the content of the law itself. This is essentially a dynamic situation, not a static one, for two reasons. The "rst is the negotiation aspect that is central to the lawyer's work, especially in commercial law domains. Legal reasoning is still involved, but reasoning about what to do with (or indeed within) the law is now at least as important as reasoning about the law itself. As such, the models that are required must represent process as well as content. This makes them fundamentally di!erent from much existing AI work. Unfortunately, this task of reasoning from a dynamic knowledge base is not one that current AI systems are typically very good at. Accordingly, the models of this type to be described in this paper di!er from those of more &&typical'' legal AI systems. They have more in common with AI planning systems than the deductive assessment systems more often seen in legal domains. A second important di!erence is the way in which the models are to be used. The authors believe that in process-based work such as that of the lawyer, the role of the model must be to provide decision support, not to make the decision. This is because, in principle, every legal case or &&matter'' is di!erent, especially in a Common Law system, and the lawyer must make strategic decisions in this light. To borrow a phrase originally intended to describe management, lawyers operate in &&a world in which nothing ever happens twice'' (Rivett, 1983). Although there is considerable scope for the use of AI techniques in modelling legal knowledge, as will be discussed, the techniques must be subservient to the lawyer's choice of strategy; a choice that may have far-reaching consequences. Previous work has demonstrated that the development of systems from this standpoint is possible; including the prototype legal knowledge-based systems (KBS) SALES CONTRACTOR and CONTRACT NEGOTIATOR (Akroyd & Edwards 1995a, b; Edwards & Akroyd, 1995). The principles of the approach to be described here apply to all Common Law systems, although the paper concentrates speci"cally on that of England and Wales. The structure of the paper is based on a model of &&rhetorical legal logic'', i.e. the lawyer's approach to a case, in the form of a double syllogism. The "rst section makes the case for such a treatment. This is done in some detail, because it is an aspect rarely considered in investigations of legal reasoning, with rare exceptions such as the article by Smith (1996). The overall process model is then presented in three complementary forms, demonstrating both a fundamental symmetry and a signi"cant asymmetry between the two syllogisms. The latter relates to the use of inductive, rather than deductive, reasoning. The argument is also put forward that most existing legal KBS work lies within one of the two syllogisms only. The second section considers the model of the "rst section in the light of the CommonKADS terminology and structure (Schreiber, Wielinga, Akkermans, Van de Velde & de Hoog, 1994). The interaction problem between domain and control knowledge is argued to be at its most severe in Common Law systems. In particular, the strategic knowledge, seen as a crucial element of the problem-solving method in the Expertise Model, is so central to deciding what must be done that it a!ects the task knowledge part of the Expertise Model, and these links may also involve the Task Model, the Organizational Model and the Agent Model. The implications of this for knowledge engineering are discussed, including the cyclical overlap of planning and assessment tasks in a lawyer's work. The use of the models for decision support, rather than fully automating decisions, is seen to be critical in managing this interaction problem.
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In the light of the importance of the strategic choice, and the decision support role of the system, it is therefore clear that most legal reasoning systems must be designed for a specialist user*a lawyer or other fee earner*to use, not for lay people. The view of the authors is that su$cient separation of domain knowledge and task knowledge may be achieved for useful modelling of both process and content to be accomplished, but that a great deal of work still remains to be done.
2. The role of the lawyer The emphasis here, as it will be throughout this paper, is on decision. Lawyers may thus be seen as strategic decision support intermediaries between a captive market population of &&customers'' for legal services and a monopoly sovereign state &&supplier'', providing advice and advocacy in negotiating legitimate relationships and resolving disputes. In doing so, however, the lawyer must attempt to respect both the aspirations of a client to have his/her unique circumstances taken into account and the requirements of the sovereign jurisdiction for a coherent, predictable, normative system, by reconciling the normative paradox between the individuality of experience and the predictability of normative systems. Aristotle de"ned justice as treating all like cases alike, but if there are no like cases, and normative systems treat unlike cases as alike, for the purpose of treating them similarly, then normative systems are inherently unjust. This is not a simple matter of trade o! between the desirable and the achievable. We can note with Oliver Wendell Holmes that: &&The training of lawyers is a training in logic. The process of analogy, discrimination and deduction are those in which they are most at home. The language (our italics) of judicial decision is mainly the language of logic. The logical method and form #atter that longing for certainty and for repose which is in every human mind but certainty generally is illusion and repose is not the destiny of man.'' (Novick, 1995)
However, as has been pointed out elsewhere, the logic referred to here is not the same as either mathematical logic or computational logic (Greinke, 1994). Nor is it the same as deontic logic (Susskind, 1987), despite the amount of consideration that has been given to it in legal reasoning. The phrase &&rhetorical logic'' is suggested, to capture the #avour of the presentation of legal argument. Although they may be seen to specialize in particular "elds, lawyers cannot choose their clients' &&matters''. Nor are English lawyers generally allowed to reject a client whose case may be hard to present successfully, however unpopular or hard pressed that client may be. The process of an adversarial lawyer's work, especially advocacy, is thus more concerned with rhetoric or argument than with the justice or injustice of a cause. The legal decision process is a complex one in which sequential sub-processes shape decision outcomes. In Common Law systems, the doctrine of precedent, which arose out of the customs of the judiciary, is crucial. There are three key elements in the Common Law process of rhetorical logic. f f f
Pleadings*de"ning the issues. Legal authorities*both statute and case law. Evidence of the facts.
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FIGURE 1. The double syllogism*&&logical'' form.
Formally, the sequencing arises from the process of legal &&proof'', which moves from issue to issue within the "elds of law and evidence in dispute, albeit with much iteration and backtracking. These interactions have been described elsewhere (Akroyd and Edwards, 1995a, b). This sequence is modelled in this paper in the form of a double syllogism, as shown in Figure 1. This is a characteristic skill in the marshalling of arguments, which is central to the work of the legal profession in all Common Law systems (Smith, 1996). Each syllogism has two premises. In the "rst syllogism, the "rst premise represents the desired decision outcomes from any disputed issues. The second premise represents legal authorities; the perceived precedents giving rise to the desired outcomes (rather than less desired or undesired ones). The conclusion is a characterization of circumstances within the law of evidence; what evidence of what &&facts'' is needed, or not needed? In the second syllogism, the order is reversed. The "rst premise now represents characterized circumstances within the law of evidence*&&the evidence''; the second premise again represents legal authorities/perceived precedents, giving rise to the conclusion, the desired decision outcomes from any disputed issues. Thus, the "rst part of the process is open-ended and characterized by the word &&because''; an essentially inductive operation. The second is closed-ended and characterized by the word &&therefore''; an essentially deductive operation. In both parts of the process, the law plays a central role, providing a common element with both the "rst premise and the conclusion; in both parts the legal authorities/perceived precedents formally constitute the syllogism. The diagrammatic form in Figure 2 suggests how each premise will in fact be made up of many part conditions; although these will by no means necessarily follow a simple production rule structure, production rules will be used by way of illustration in the remainder of the paper. The &&double-syllogism'' model provides an aesthetically pleasing degree of symmetry, as is emphasized in its third form; the diamond shown in Figure 3. This "gurative representation also avoids specifying the detail too precisely. However, there is also a signi"cant asymmetry between the two syllogisms, in the form of the role played by the precedents in the two parts, which is substantially similar rather than opposite. This is where the double syllogism di!ers from simple backward and forward chaining by deductive inferencing, in the inductive role of the precedents in the "rst syllogism. This will now be explained further.
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FIGURE 2. The double syllogism*expansion into part conditions
These two key sub-processes in syllogistic legal argument can conveniently be labelled: (1) &&tracing the antecedents of the decision'' and (2) &&establishing the consequences for the decision''.
2.1. TRACING THE DECISION'S ANTECEDENTS (SUB-PROCESS A)
This is a research-based exercise. Precedent has not been widely considered in the legal AI or KBS literature. In Common Law systems, it is not simply a question of identifying precedents in the form of relevant cases by using a similarity measure as a case-based reasoning system would. There is a place for such an activity, and there may be scope for using such a system, but the important point lies in the phrase perceived precedent. Tracing the decision's antecedents is capable of heuristic, inductive use, both by the lawyers involved in preparing a case and indeed the judges called upon to give judgement in it. The potential for the heuristic use of precedent arises from the impossibility of an exact match between any two case circumstances, combined with an increasing plethora of potential analogies, as the database of case precedents continues to grow, apparently exponentially. The tendency for heuristics (in the strictest sense of the term, as rules of thumb used by many) about legal principles to arise in opposing/contradictory pairs, as discussed by Smith (1996), provides a further incentive for inductive reasoning. Deductive reasoning with such a rule set would be fruitless.
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FIGURE 3. The double syllogism*"gurative representation.
The inductive heuristic process is subtle. It begins with what situation(s) or remedies the client wants. It then goes on to ask what combination of legal criteria supported by case precedents will give such a desired outcome. The criteria are invoked, if at all, only by admissible and convincing evidence of often subtly distinguished circumstances. The subtlety here is that the proposition inferred is not, as might be imagined, solely one of substantive legal principle, but also of provable situation, a conclusion of evidence speci"c to the particular case. It is the rhetorical characterization of a client's case that is at the root of legal argument. Thus, the process of induction from one precedent to legal and evidentiary principle is a double one. It is based on characterization with hindsight of the supposed reason for a decision (ratio decidendi) on legal and/or evidentiary matters actually in issue. This hindsight is not the simple deduction of backward chaining, "nding sequences of rules that exist. It is a covertly creative activity, equivalent to modifying the rules or "nding
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new ones, to yield the most convincing path to a &&necessary'' decision. This asymmetry makes the double syllogism necessary, and this important distinction has given rise to the creative uncertainties of stare decisis so clearly revealed by the judicial career of Lord Denning, and the essentially adversarial Common Law process of dispute by advocates. Note that, for clarity, the examples that follow are all chosen from the arguments of judges rather than those of lawyers which, although also available in law reports, are presented in an overtly adversarial manner, bringing a further degree of complexity. In Common Law jurisdictions, however, judges are appointed solely from the ranks of lawyers experienced in the same mode of reasoning. In Harper v NCB [1974] 1 QB 614, 618 et seq., Denning MR was faced with the seemingly intractable problem of having to follow an inconvenient binding precedent of the House of Lords. His line of reasoning displays characteristic ingenuity, and evidence of the double syllogism in action: &&We can only accept a line of reasoning which supports the actual decision of the House of Lords. By no possibility can we accept any reasoning which would show the decision itself to be wrong. The second proposition is that if we can discover the reasoning on which the majority based their decision, then we should accept that as binding upon us. The third proposition is that if we can discover the reasoning on which the minority based their decision we should reject it. It must be wrong because it led to a wrong result. The fourth proposition is that, if we cannot discover the reasoning on which the majority based their decision, we are not bound by it. We are free to adopt any reasoning which appears to us correct, so long as it supports the actual decision of the House 22''
Denning's "rst three propositions follow deductive logic through to its limits with the existing rule set. The fourth proposition "nds the existing rule set insu$cient for the task, and invokes an inductive step to devise new rules. Denning continues: &&Applying the propositions to Smith v Central Asbestos Co. Ltd. (Dodd's case), [1973] AC 518, the position stands thus: (1) the actual decision of the House in favour of Dodd must be accepted as correct. We cannot, accept any line of reasoning which would show it to be wrong. We cannot, therefore, accept the reasoning of a minority of two*Lord Simon of Glaisdale and Lord Salmon*on the law. It must be wrong because it led them to the wrong result. (2), we ought to accept the reasoning of the three in the majority if we can discover it. But it is not discoverable. The three were divided. Lord Reid and Lord Morris of Borth-yGest took one view of the law. Lord Pearson took another. We cannot say that Lord Reid and Lord Morris of Borth-y-Gest were correct: because we know that their reasoning was in con#ict with the reasoning of the other three. We cannot say that Lord Pearson was correct: because we know that the reasoning which he accepted in the law led the other two (Lord Simon of Glaisdale and Lord Salmon) to a wrong conclusion. So we cannot say that any of the three in the majority was correct. (3), the result is that there is no discernible ratio amongst the majority of the House of Lords. In these circumstances I think we are at liberty to adopt the reasoning which appears to us to be correct.''
The manipulation of precedent arises out of situations where either: (1) there is a need to create &&decision space'' within an over-abundance of case law precedents (&&too many rules'') or (2) there is an over-riding need for any &&colourable authority'' (relevant precedent) and the precedents are few and/or weak (&&too few rules''). (1) Where there is an over-abundance of precedents.The key skills in this process stage are the reconciling of apparently con#icting decisions and the distinguishing of apparently similar case situations.
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In fact, these apparently distinct skills are the &&two sides of the coin'' of a single high-level task that includes aspects of both assessment and planning, as will be discussed in more detail later. A major example of the reconciliation of apparently con#icting decisions is Lord Denning's long-running battle to establish that, where the creative construction of evidence &&revealed'' a broken fundamental term in a contract, a rule of law prevented any exclusion of contractual liability. In the Suisse Atlantique Case [1967] 1 AC 361, a conservative House of Lords eventually held unanimously in favour of a more elegant alternative. Accordingly, where evidence of the whole agreement, including any exemption clause, revealed its fundamental breach, it was a matter of fact rather than of law, that the exemption clause was necessarily too narrow to cover the breach. This approach had the additional advantage of including multiple minor, but damaging breaches. However, because exclusion clauses had not been directly in issue in the Suisse Atlantique Case, the judgement could be characterized as merely persuasive (obiter dictum) rather than binding. Hence, in Farnsworth Finance Facilities v Attryde [1970] 2 All ER 708, Denning MR was able to reassert his own doctrine as wholly consistent with the judgement of the House of Lords (sic), for the purpose of preventing an exclusion of liability, where the aggregation of minor defects in a motor cycle had rendered it virtually useless. E!ectively, this is denying the existence of a rule that might appear to some to be in the rule set. An example of a distinction being made between apparently similar case situations is the judgement of the Court of Appeal in Lewis v Averay [1972] 1 QB 198, distinguishing its circumstances from those of its earlier decision in Ingram v Little on the basis of an arguable distinction between identity itself and such attributes of identity as fame, wealth and so on. According to English legal principle, where fraud induces an original owner of property to contract on the basis of mistaken personal identity, the contract will be void, enabling them to reclaim the property. If the mistake was one of personal attributes such as credit worthiness, however, the contract will be voidable only, requiring the original owner to complete some further act of &&avoidance'' before some innocent third party acquires proprietary rights. As Lord Denning says at [1972] 1 QB 206, this is a distinction without a di!erence. The means of checking identity are rarely e!ective or logical. In Ingram v Little [1961] 1 QB 3l, the original owners' act of checking an interim dealer's identity by looking up his (false) name in a telephone directory formed the basis of the Court of Appeal's decision, thereby allowing the original owners to reclaim their car, as being sold under mistaken identity. In the very similar Lewis v Averay [1972] 1 QB 198, the original owners were only persuaded of the interim dealer's identity by checking his (false) name, picture and other details on a forged "lm studio pass, but nevertheless could not reclaim their car as being under a mistake as to attributes only. A rule had been &&invented'' to distinguish the two situations. (2) Where precedents are few or weak. Sometimes, moreover, legal decision shapers are faced with the converse situation where, the most diligent research having failed to reveal any genuinely convincing precedent, the heuristic proceeds on the basis of &&colourable'' (barely acceptable) authorities and/or those of weight but little direct relevance. In Ray5eld v Hands [1960] Ch 1, for example, the then Companies Act contained provision for a company's memorandum and articles, when registered, to bind the
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company and the members, as if they contained covenants to observe all of their provisions on the part of each member. In fact, one private company's articles required any member intending to transfer shares to inform the directors &&who will take the said shares equally between them at fair value''. The directors were also members by virtue of their quali"cation shares. One such member did so inform the directors and, on their refusing to purchase his shares, brought an action for a declaration that they were bound by the article to do so. The plainti!'s case rested on three issues: on the "rst two, Vaisey J. held conventionally in favor of the plainti!. On the third, he concluded: &&On the whole if22the maxim &validate if possible' applies, I think that the plainti! in this action ought to succeed. Not one of the judges in Dean v Prince [1954] Ch 409 showed any sign of shock or surprise at the assumption there made of a contract between directors being formed by the terms of a company's articles.''
That is, of course, true, but that assumption was made on an issue which was never actually raised in Dean v Prince. It could not, therefore, constitute a precedent for Vaisey J.'s proposition. But how else would he have been able to give judgement for the plainti!? Here, conditions and consequences already present separately in the rule set have been joined in a new way to form a new rule. 2.2. ESTABLISHING THE DECISION'S CONSEQUENCES (SUB-PROCESS B)
By working backwards from the widest possible starting point (i.e. the perception of factual evidence) and proceeding apparently inexorably, via the relevant authorities, to a seemingly inevitable outcome, the open-textured, research-based sub-process A becomes the closed exercise in apparently conventional logic of sub-process B. Sub-process A is often unstated in a legal matter, perhaps even barely conscious, whereas sub-process B is invariably evident. Hence, what initially begins as an open, highly discretionary process is presented as a closed, almost mechanical, process, thereby satisfying both the imperative towards personal sensitivity and that towards normative consistency in judicial decision making. In certain types of situation, this may be signi"cantly varied. In a human rights situation, for instance, where a neo-natural law approach is necessary, sub-process A will be very obvious. On the other hand, in a commercial context, sub-process A will tend to be suppressed in favour of the positivist approach of sub-process B. This is somewhat similar to the well-known &&scru!y/neat'' distinction between pragmatic and doctrinal thought in AI usually "rst credited to Roger Schank. However, there is one crucial di!erence; as stated above, the two sub-processes are not &&either/or'' aternatives. Both sub-processes exist in all legal &&matters'', even though sometimes one dominates the other. Some approaches, for example those just described, "t more closely to one sub-process or the other, and this is mirrored in much existing legal reasoning work. It is scarcely surprising that legal KBSs have tended to concentrate on sub-process B. Fortunately, however, the American realist approach for example, is amenable to both sub-processes (Smith, 1996). 2.2.1. Process support Figure 4 shows the diamond of Figure 3 with the additional adversarial component incorporated, although it should be noted that the overlap of the two diamonds is by no
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FIGURE 4. The double double syllogism (sic)*the plainti! and the defendant.
means necessarily largest near the boundary between sub-process A and subprocess B, as it appears to be in the "gure. Indeed, key skills of the Common Law advocate's rhetoric include justifying their own desired rule set for sub-process B, and anticipating the possible rules set that their adversary might have produced in subprocess A! More detailed process modelling of the three key elements (pleadings, legal authorities and evidence) is beyond the scope of our discussion here. Much of it does not require knowledge engineering in the narrow sense, in that the computer support required is best provided by conventional, rather than knowledge-based systems. For example, the most useful tool in the presentation of pleadings is likely to be a good word processing package, and the speed of e-mail or EDI systems may be highly bene"cial in the transfer of documents or evidence, as long as such systems are admissible!
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3. A CommonKADS perspective on the double-syllogism model CommonKADS (Schreiber et al., 1994; Van Heijst, Schreiber & Weilinga, 1997) has become the de facto European standard approach to knowledge engineering. Its predecessor KADS has been used in the legal domain (Breuker, 1993) to develop an architecture for legal reasoning, TRACS. The TRACS architecture, described further in den Haan (1993, 1996) is designed to support the drafting of legislation. It distinguishes between reasoning about a case and reasoning about legal consequences, by a separate representation of world knowledge and normative knowledge. This mirrors the symmetry of the double-syllogism model to a certain extent, but does not speci"cally include the role of perceived precedents as it is intended for a Civil Law system, the &&legal world'' being modelled essentially as &®ulations''. For example, den Haan (1996) uses TRACS to evaluate the Dutch Tra$c Regulation RVV1990. Breuker (1993) asserts that most legal reasoning tasks fall under the heading of assessment tasks, thus demonstrating the value of the TRACS architecture, since it &&maps easily onto the KADS conceptual model of the assessment''. However, it is proposed here that, at least in Common Law systems, this is too narrow a view of what legal reasoning entails, as will be explained below. Interestingly, den Haan (1996) proposes the extension of TRACS so that it could be used in drafting legislation, a task which would have a closer similarity to the double syllogism. The whole philosophy of CommonKADS is one of knowledge modelling, as opposed to earlier approaches to developing knowledge-based systems, whose paradigm was often closer to that of extracting knowledge from the human expert(s), with all the pain that term implies. CommonKADS comprises a suite of no fewer than six types of model. f f f f f f
Organisational model. Task model. Agent model. Expertise model. Communication model. Design model.
CommonKADS also speci"es the nature of the linkages between these six types of model. In general, all six types of model will be present in any use of CommonKADS, although it is perhaps fair to say that the Expertise and Communication Models are the most developed. The question for knowledge engineers is whether this decomposition is appropriate, or at least adequate, for knowledge modelling in a particular domain. This will now be examined in the light of the proposed double-syllogism model, and the decision support role of the system. 3.1. THE INTERACTION PROBLEM IN COMMON LAW DOMAINS
A central problem in knowledge-based systems relevant to any kind of decomposition has been the extent to which domain knowledge can be separated from control or task knowledge. This separation was claimed as one of the advantages of early rule-based
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expert systems and the expert systems shells that followed. However, it was seldom if ever achieved in practice, and this led Bylander and Chandrasekaran (1988) to state that a complete separation could not be achieved; the so-called interaction problem. KADS originally attempted to achieve this complete separation, but CommonKADS now incorporates a relative interaction hypothesis*that di!erent types of knowledge di!er in the degree to which they are dependent on the task. The domain knowledge may therefore be thought of as a layered set of ontologies or metamodels, each layer comprising knowledge with the same degree of task dependence. The six types of model, together with the relative interaction hypothesis, give a very rich structure for representing not only knowledge, but the organizational context in which the KBS is to be used. Knowledge engineering thus takes on the wider sense of the complete design and development of the system, not just &&putting the expertise in'' any knowledge-based components. However, there are two aspects in which CommonKADS does not yet appear to be su$ciently developed to model the domain of the lawyer's work completely: f f
Level of task de"nition. Modelling of domain knowledge.
Tasks in CommonKADS, as in its predecessor KADS, form a hierarchy of tasks and sub-tasks, in order that a &÷ and conquer'' approach may be taken (Harris-Jones, 1995). The lowest-level tasks, the primitives, typically correspond to the inference functions in the expertise model; tasks such as &&select'' and &&compare''. These are then combined hierarchically to make up the overall task of the KBS. In addition to task and domain knowledge, the expertise model contains problem-solving methods and strategic knowledge. The problem-solving method prescribes how the task de"nition is mapped onto the task body, i.e. how the task is to be carried out. A library of problem-solving methods exists (Breuker & van de Velde, 1994), covering nine problem types including assessment, diagnosis and planning. In principle, the strategic knowledge allows integration of the problem-solving methods as an explicit part of the expertise model, to allow the KBS to decompose the task dynamically. However, the task that a lawyer in a Common Law system might wish a KBS to perform is, it is argued, not so easily speci"ed. The CommonKADS structure posits that the organizational model is used to help identify the top-level tasks in the domain as a whole (which form the task model) and so identify appropriate agent roles for one or more KBSs, with an agent model for each. This assumes that the nature of the links between the organizational, agent and task models is "xed for any given context in which a KBS is used. For the lawyer in a Common Law system, this assumption appears invalid; the #exibility that exists in a Common Law system is such that the very links between tasks, agents and organizational model are not "xed; they are dynamic. Although the communication model allows for a range of interactions between the KBS and other agents, including a human user, these too need to be "xed for a given context. It is notable that Van Heijst et al. (1997) e!ectively begin knowledge modelling with the generic tasks and problem-solving methods. Consider, for example, selecting precedents meeting certain criteria from a precedents database. This is certainly a knowledge-based reasoning task, and so suitable in principle for a KBS. However, it is extremely di$cult to formulate the properties and concepts
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that would be needed to frame the criteria for selection. It is straightforward to conceive that such a list would need to include measures of the similarity of the perceived outcomes, principles and &&facts'' cases to those (desired) in the present case. However, in a Common Law system, it is also likely to be necessary to consider the seniority of the court, the weighting of judgements where applicable (such as 5-0, 4-1 or 3-2) and the personal composition of the court. (These may be thought of as forming an axis orthogonal to the "rst one.) Further, it may also be necessary to select according to elements of the sequence of the pleadings, where such information is available; another aspect of process rather than content. Thus, although the selection of precedents has similarities with an assessment or categorization task, it is not a simple case of such a task, or another task type such as a planning task. It combines assessment and planning, and perhaps diagnosis and other task types as well. The examples earlier in this paper illustrate the complex nature of what is perceived to be a relevant precedent. The relationship between assessment and planning, for example, in any particular selection task will depend on the strategic choices made by the lawyer. Yet these choices may themselves depend on the results of the task of selecting precedents, in an iterative manner. Although CommonKADS allows for recursion in the task hierarchy, it does not yet appear to encompass this high-level iteration, where the nature of the agent's task may depend on the results which that task has already produced, and the communication required may also change accordingly. The relative interaction hypothesis applies at the level of the tasks within the expertise model, not to the interaction between domain knowledge and the overall task that the KBS agent is to perform. In Common Law legal systems at least, there does seem to be such an interaction. Support for this view comes from the work of Kingston (1995). He found, in attempting to apply KADS to the use of KADS, that &&the de"nition of concepts and properties in a domain appears to be context dependent'', so that there is more than one &&correct'' model of any chosen domain. We would expect this to be the case with a Common Law system. Were it not so, then the choice of precedent would be a simple exercise in data retrieval, and there would be no room for the American realist school of thought that &&the judges make the law''. Almost every educated lay person in England over a certain age remembers the case of the drink-driving charge that failed because the police o$cer administering the test was not wearing his hat at the time. It seems an impossible task to construct appropriate problem-solving methods for the expertise model that would take such features into account routinely without guidance from the user. A decision support approach is thus needed, and it is argued that the CommonKADS model structure assuming a "xed task and role for the KBS agent is not capable of capturing this adequately, despite the range of interactions allowed for in the communication model. In a knowledge-based system providing decision support, as with all decision support systems, the relationship between the user and the system is #exible, even beyond the point of division of tasks between them; see for example Silver (1991). At the highest level, the double-syllogism model presented here is o!ering a di!erent perspective on the task, organizational and agent models of CommonKADS. Although the organizational model does include process aspects, as well as functions, it appears that it does not fully embrace the process focus of organizations in the way seen in total quality management (e.g. Oakland, 1989) or business process re-engineering (Davenport,
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1993). The processes in the CommonKADS organizational model seems to be subservient to the functions. Whilst perhaps typical of most legal services "rms until at least the 1980's, this is no longer appropriate as we approach the millennium; the authors have discussed process reengineering in legal services "rms elsewhere (Akroyd & Edwards, 1997). The rigidity that results from this function-driven perspective is limiting the usefulness of CommonKADS in developing knowledge-based components of decision support systems. In Common Law systems, a decision support approach to KBS use would seem to be essential.
4. Significance for knowledge engineering Greinke (1994) shares the conviction advanced here that the provision of decision support is a more fruitful approach to assisting lawyers than that of fully automating legal reasoning. There appears to be plenty of scope, however, for appropriate use of both; using automated, model-based legal reasoning in providing decision support. As conceived here, the whole project of developing such a system is still knowledge engineering, because the knowledge-based elements are central to the performance of the human}system &&team'' as a whole. However, the resulting system must incorporate #exibility at a very high level. It is this #exibility that CommonKADS does not appear to be able to incorporate at present. We would not claim a detailed enough knowledge of CommonKADS to be able to specify a generic form of the necessary changes yet, but in the domain of Common Law jurisdictions, we believe that the more process-focused double-syllogism model, supplementing the CommonKADS model set, will form a suitable basis for knowledge engineering.
5. Conclusion Modelling legal reasoning, and the knowledge engineering that goes with it, is often seen as essentially a task that requires development of either an inductive or deductive system, to achieve a high degree of automation of the reasoning process. The argument that has been presented here is that, at least in Common Law systems, this &&either/or'' approach is too narrow when considered from the perspective of what lawyers do. Each case or matter requires both inductive and deductive reasoning, in the context of a strategy that is developed for that case only. The appropriate mode of operation of a legal knowledgebased system is thus as a decision support system to assist the lawyer (or other fee earner). This support needs to be provided within the context of an overall model of the process in the form of a double syllogism, as has been presented in the paper. This model serves not only as a basis for legal knowledge engineering, but also to indicate where existing work "ts in. CommonKADS is seen as meeting many of the needs of legal knowledge engineers, but needing to be supplemented in designing systems to function in a decision support role. However, the overall construction of such systems is no small undertaking, being at least one level higher than most existing work. Our cumulative work on this is continuing (Akroyd & Edwards, 1995b). To, conclude, it is by no means the authors' hypothesis that the inductive/heuristic and deductive/didactic double syllogism is applicable only to systems of Common Law. On
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the contrary, it is precisely because of its general applicability within the discourse of many disciplines that the signi"cance of its adaptation by legal systems rests. Whilst at "rst sight the double syllogism seems unsuited to the academic inquisitorial culture of the Civil Law process, the deductive/didactic second syllogism is very evident. It may be, moreover, that an inductive/heuristic syllogism might be discernible implicitly at the highly generalized societal level of the drafting of the codes themselves. This might help to overcome the di$culties that Breuker (1993) identi"ed regarding modelling the social system to which and in which a set of legal regulations was intended to apply. Taken to its logical conclusion, this would imply that more complete knowledge-based systems may be feasible in Civil Law systems than in Common Law ones, although this claim is by no means proven yet.
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