Newtonianism in early Enlightenment Germany, c. 1720 to 1750: metaphysics and the critique of dogmatic philosophy

Stud. Hist. Phil. Sci. 35 (2004) 471–491 www.elsevier.com/locate/shpsa

Newtonianism in early Enlightenment Germany, c. 1720 to 1750: metaphysics and the critique of dogmatic philosophy Thomas Ahnert Institute for Advanced Studies in the Humanities, University of Edinburgh, Hope Park Square, Edinburgh EH8 9NW, UK

Abstract The acceptance of Newton’s ideas and Newtonianism in the early German Enlightenment is usually described as hesitant and slow. Two reasons help to explain this phenomenon. One is that those who might have adopted Newtonian arguments were critics of Wolffianism. These critics, however, drew on indigenous currents of thought, pre-dating the reception of Newton in Germany and independent of Newtonian science. The other reason is that the controversies between Wolffians and their critics focused on metaphysics. Newton’s reputation, however, was that of a mathematician, and one point, on which Wolffians and their opponents agreed, was that mathematics was of no use in the solution of metaphysical questions. The appeal to Newton as an authority in metaphysics, it was argued, was the fault of Newton’s over-zealous disciples in Britain, who tried to transform him from a mathematician into the author of a general philosophical system. It is often argued that the Berlin Academy after 1743 included a Newtonian group, but even there the reception of Newtonianism was selective. Philosophers such as Leonhard Euler were also reluctant to be labelled ‘Newtonians’, because this implied a dogmatic belief in Newton’s ideas. Only after the mid-eighteenth century is ‘Newtonianism’ increasingly accepted in the sense of a philosophical system. # 2004 Elsevier Ltd. All rights reserved. Keywords: Natural philosophy; Mathematics; Metaphysics; Isaac Newton; Newtonianism; German Enlightenment

E-mail address: [email protected] (T. Ahnert). 0039-3681/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.shpsa.2004.06.003

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1. Introduction The works of Isaac Newton were read and discussed in Germany from the very beginning of the eighteenth century. Leibniz criticized Newton’s theory of gravitation in his Theodicy, as did Christian Wolff in a reply to John Keill. Newton’s optics were defended by a Professor Richter in the Leipzig Acta Eruditorum against the criticisms of an Italian natural philosopher, Giovanni Rizetti. German interest in Newton’s mathematical writings was guaranteed by the priority dispute, especially after Newton had instigated the condemnation of Leibniz by the Royal Society for plagiarism in 1712. Moreover, a survey of the Acta Eruditorum in the first decades of the eighteenth century also reveals a number of reviews of Newton’s works.1 There was, therefore, at least some familiarity with specific Newtonian doctrines from an early stage. But in general the reception of Newton’s ideas was ‘hesitant and slow’ in Germany, as on the European continent as a whole.2 The reluctance to embrace Newtonianism, Jonathan Israel has argued, constitutes ‘a meaningful historical problem on its own’.3 The purpose of this article is to examine this slow reception of Newton’s ideas and ‘Newtonian philosophy’ in the early German Enlightenment. It is usually argued that Newtonian doctrines began to be propagated in Germany only from the 1740s by Leonhard Euler and other critics of Wolff at the Berlin Academy of Sciences.4 Here it will be suggested that the emergence of Newtonianism in the German states was less abrupt and clearly defined than that. Part of this article, therefore, will be on the dissemination of Newtonian doctrines in the early German Enlightenment. However, the history of Newtonianism in that period must not only include an examination of the extent to which particular, recognizably Newtonian ideas were accepted or opposed. It also needs to take into account the more general sense in which the terms ‘Newtonianism’ and ‘Newtonian philosophy’ were understood by contemporaries. What did Newtonianism represent in the opinion of early eighteenth-century Germans, including those who were not ‘Newtonians’ themselves? Was it restricted to specific mathematical and natural philosophical doctrines, or did it describe a more general philosophical system or method? If so, what system did it stand for? Until about the middle of the eighteenth century opinions on such a wider Newtonianism almost seem to foreshadow a twentieth-century philosopher’s judgement that Newton was ‘a marvellous genius’ in ‘scientific discovery and formulation’, 1

Leibniz (1952), pp. 85–86; Wolff (1710). Leibniz and Wolff criticized gravitation as an example of a qualitas occulta (Richter, 1724). On the priority dispute see Hall (1980), pp. 178–179. Newton’s mathematical theories were the subject of reviews in the Acta of 1705 and 1708. A review of the second edition of the Principia appeared in 1714. Newton’s optical theory was discussed in 1706. 2 Israel (2001), pp. 523, 557. 3 Ibid., p. 523. For a classic study of ‘Newtonianism’ in the early English Enlightenment see Jacob (1976). 4 Israel (2001), p. 557.

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while ‘as a philosopher he was uncritical, sketchy, inconsistent, even second-rate’.5 While Newton’s narrowly scientific works were widely admired, even by those who disagreed with him, many dismissed the idea of a ‘Newtonian philosophy’ altogether. ‘Newtonian philosophy’, these critics argued, had little to do with Newton. It had been invented by self-declared followers of Newton, such as Voltaire in France or Henry Pemberton in England, who dogmatically tried to turn Newton’s ideas into the foundation of a comprehensive philosophical system. What Newton’s ideas lacked, in particular, it was argued, was a metaphysical foundation. Without this foundation, Newtonian mathematics and natural philosophy did not add up to a system of ‘Newtonian philosophy’. But why was Newton not recognized as a metaphysician?

2. A Newtonian metaphysics? Newton and the Leibniz–Clarke correspondence in Germany The question whether Newton was a metaphysician was first raised in Germany by the publication of the Leibniz–Clarke correspondence. This appeared in London in 1717, but it was considered important enough to be published in a German translation in 1720, for which Christian Wolff himself wrote a preface and Wolff’s pupil Ludwig Thu¨mmig added a response to Clarke’s fifth reply.6 Metaphysics and natural religion were the main subjects of the correspondence. One of the arguments Leibniz put forward in it was that space was defined by the relation of material bodies to each other. Without the presence of extended bodies space did not exist. Clarke argued that space was a real entity (spatium absolutum reale), even in the absence of any corporeal entities.7 A similar disagreement between the two philosophers focused on the nature of time. Leibniz believed time was defined by the succession of events, whereas Clarke wrote that time existed independently, that is, even in the absence of a succession of events.8 This meant that in Clarke’s view God could have created a world identical to this in another place at another time. However, Leibniz believed that it would then be impossible to provide a reason why God had created the world at that particular time and place. In such a case God would have acted without a sufficient reason.9 Leibniz argued that this was impossible, on two grounds. One was that for every action there had to be a sufficient reason. The will, which took the decision in favour of a particular action, was not truly indifferent. If it were, it would be like a perfectly balanced pair of scales, which never inclined to either side.10 The second ground was that God in particular, the infinitely wise and 5 6 7 8 9 10

Burtt, quoted in Buckle (2001), p. 208. Clarke (1720). Ibid., p. 30. Ibid., pp. 31–32, 124. Ibid., p. 30. Ibid., p. 65.

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good creator of the world, had to be acting on the basis of morally good reasons, when he created the world. Acting without such reasons contradicted divine nature itself, which was the highest form of moral goodness, based on reason.11 A God who acted without sufficient reasons would be a tyrant, an argument which Leibniz also drew on in his critique of Pufendorf’s natural jurisprudence.12 Although human reason was infinitely weaker than God’s, the difference between the two was one of degree, not quality. To a limited extent, therefore, God’s actions could be understood and explained by mortals.13 Clarke contradicted Leibniz, saying that a decision taken by the will did not simply reflect a particular sufficient reason. The will was an active capacity for choice. In both human and divine affairs there was often no particular reason for a certain action other than that it was decided on by the free will. Moreover, God’s decisions were ultimately inscrutable to the feeble human intellect, so that any attempt to speculate about the nature of God’s motives was futile.14 Clarke, like other theological voluntarists such as Robert Boyle, regarded this freedom of divine volition to act without a reason, or at least without a reason accessible to human understanding, precisely as a sign of divine omnipotence.15 Clarke and Newton also believed it possible and even necessary for God to intervene directly in the government of the natural world. These interventions were necessary, for example, in order to replenish the world with the motive force lost in collisions between material bodies. Without this divine intervention the world would eventually come to a standstill.16 But whereas Clarke and Newton regarded interventions of this kind as proofs of divine power, Leibniz argued that they had to be superfluous. The amount of motive force in the world was constant and no divine interference was necessary to maintain its level. If God governed the world by intervening in particular cases, rather than by immutable laws established by himself in creation, he was like a second-rate watchmaker, who continually had to repair, clean and rewind his clocks, rather than constructing them with such skill that they functioned without interference.17 Newton and Clarke, however, both denied the existence of eternal laws in the Leibnizian sense, into which humans had any insight on the basis of their rational faculties. God did not act according to such laws and the normal course of nature was not defined by such laws. There was no difference in principle between the ordinary course of nature and supranatural divine intervention. As Clarke said, the ‘terms, nature, and powers of nature, and course of nature, and the like, are nothing but empty words; and signify 11

Ibid., p. 54; Riley (1996), p. 16. Hochstrasser (2000), p. 74. Leibniz (1988), p. 50. 13 Riley (1996), p. 15. 14 For a reassessment of the relationship between voluntarism and early modern science, see Harrison (2002). 15 Clarke (1720), p. 169; Boyle (1996), p. 160. On the relationship between Boyle’s natural philosophy and his religious beliefs see Wojcik (1997). 16 Clarke (1720), p. 44. 17 Ibid., p. 35. 12

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merely, that a thing usually or frequently comes to pass’.18 The only substantial difference between natural procreation and the resuscitation of the dead, for example, was that the former was more common than the latter. Leibniz’s emphasis on the government of creation by eternal rational laws was closely related to his attempt to reconcile the idea of divine goodness with the presence of evil in the world. Leibniz had addressed this question already in his refutation of the French Huguenot Pierre Bayle. Leibniz objected in particular to Bayle’s conclusion that the presence of evil in the world was incompatible with human standards of goodness, but that what appeared to be evil from a finite human perspective was founded in God’s inscrutable wisdom.19 In his Theodicy Leibniz had set out to prove that God did act according to eternal moral laws, of which humans had a limited understanding on the basis of their reason. God’s definition of morality and that of humans were therefore compatible. God as the supremely just being also wanted the good absolutely, but in the created world the possible instantiations of morally good states of affairs were limited by the principle of ‘compossibility’, that is, the logical compatibility of different good states of affairs. The existence of one good could preclude the existence of another. This incompatibility was the origin of evil. In such cases God chose the better or less bad of two conditions, in such a way, that although creation was not a world in which everything was good, it was the best of all possible worlds and that in which the amount of evil was minimized.20 God’s conscious choice of the best of all possible worlds meant that everything in the world had to be determined at the moment of creation, including the actions of individuals. Clarke objected that this amounted to fatalism. Individuals could not be held responsible for their actions if Leibniz’s theory were true.21 Leibniz denied the charge of fatalism, saying that God did not coerce humans to act in a particular way, but instead chose to instantiate those persons who acted without external compulsion according to the principle of the best of all possible worlds. Leibniz’s argument was related to his theory of free will. The will was not free in the sense of being indifferent to its various possible choices. Its decision was always determined by a sufficient reason. It was free only in the sense of being spontaneous, that is free from external compulsion (although the actions related to that will could of course be restricted by external circumstances). Leibniz therefore could assume that each individual instantiated by God would act in a certain way, but that this form of predetermination could also be reconciled with his theory of the freedom of the will.22 In order to explain the relationship between the physical body and the human soul Leibniz put forward the notion of a pre-established harmony (harmonia 18

Clarke (1998), p. 114. The equivalent passage in the German translation is on p. 211 in Clarke (1720). 19 Leibniz (1952), passim; Labrousse (1983). 20 Riley (1996), p. 76. 21 Clarke (1720), p. 65. 22 Clarke (1998), p. 85.

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praestabilita) between the two, an idea which only confirmed Clarke’s suspicion of fatalism. According to Leibniz, bodily motion was purely mechanical and governed by the motive forces of physical matter. The body was not directed by the human soul. The activities of the soul, that is, its thoughts and its sense perceptions, were necessary, but they were determined by their own internal principles of change, independent of physical matter. The development of souls and that of bodies, however, were closely co-ordinated with each other. The intention to lift an arm, for example, coincided with the act of lifting it, so that although soul and body functioned independently of each other, they appeared to be related because of the close correspondence between their actions. This correspondence was the harmonia praestabilita.23 After Leibniz’s death in 1716 Christian Wolff took up his cause against Clarke. In his preface to the German edition of the correspondence, Wolff defended Leibniz by arguing that Clarke clung to sense perception and the imagination rather than following reason. Sense perceptions were not the basis of truth, but only a shadowy representation of it. They did not lead to certain knowledge, which had to be based on ‘allgemeine Begriffe’, that is eternal rational truths. The adherence to sense perceptions bred the ‘common prejudices’, which obstructed progress in metaphysics.24 Thu¨mmig in his response to Clarke’s fifth reply argued in a similar fashion that many philosophers overvalued sense impressions and neglected the concepts derived from unambiguous rational principles. As he wrote in his contribution, it was clear that ‘one clings too much to the imagination and is content with mere images instead of the clear concepts, which are derived by correct deductions from clear principles of reason, such as the principles of contradiction and of sufficient reason, through which illumination is brought about in metaphysics’, an error, he added, to which Locke also had been prone in his Essay on human understanding.25 3. Newtonianism, metaphysics and the German response to Wolff, ca. 1720 to 1740 The issues on which Leibniz and Clarke had focused in their correspondence were central to the debates among German philosophers in the first half of the eighteenth century. Leibnizian–Wolffian metaphysics, natural religion and moral philosophy were strongly criticized by a series of prominent philosophers and theologians, such as Georg Ernst Stahl (1659–1734), Johann Franz Budde (1667–1724) or Joachim 23

Ibid., p. 85. Wolff writes that ‘[d]er Herr Clarke haenget noch sehr an den Sinnen und der Einbildung/ daraus die gemeinen Vorurtheile fliessen/ wodurch die Wahrheit in der Metaphysick aufgehalten wird’ (Clarke, 1720, ‘Vorrede’). 25 Thu¨mmig wrote that ‘man noch gar zu sehr an der Einbildung haenget und an statt der deutlichen Begriffe, welche aus klaren Gruenden der Vernunfft, dergleichen die Principia contradictionis und rationis sufficientis sind, dadurch in der Metaphysic das Licht angezuendet wird, durch richtige Folgerungen hergeleitet werden, sich mit blossen Bildern vergnueget’ (Clarke, 1720, p. 253). 24

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Lange (1670–1744). The question of the nature of God’s power over the world, the limits of human reason, the definition of free will and the relationship of the body to the soul in particular were the subject of many controversies. And yet, these debates are notable for the absence of references to Newton or even Clarke. Occasionally, critics of Wolff showed that they were aware of Newtonian theories, but they did not use them in connection with their critique of Wolffian philosophy and especially metaphysics. There appear to be two reasons for this lack of interest in Newton as a metaphysician, even among anti-Wolffian philosophers who could have enlisted him on their side of the controversy. The first is that Wolff’s opponents could draw on a variety of arguments, which pre-dated the reception of Newton’s ideas and the Leibniz–Clarke debate. Although similar to Clarke’s ideas in some respects, it is clear that these arguments of Wolff’s German opponents were not derived from Clarke’s writings and, moreover, did not depend on a specifically Newtonian natural philosophy or mathematics to be considered persuasive. One of Wolff’s most formidable opponents, for example, was Joachim Lange, a professor of theology at the University of Halle. It was Lange whose critique of Wolff’s philosophy was to a large extent responsible for the expulsion of Wolff from his university post and the territories of the Elector of Brandenburg in 1723.26 Lange’s main critique was that Wolff’s metaphysics led to fatalism. Lange defended a view of the freedom of the will, which was similar to that of the early Christian Thomasius in the Institutes of divine jurisprudence of 1688.27 A central part of Lange’s argument was his critique of Wolff’s equation of freedom and spontaneity of the will. Wolff, like Leibniz, had argued that the human will was free because it was spontaneous, that is not determined by anything external to the human soul, although it was determined by its own internal principles of development. There always had to be a sufficient reason for a particular volition. It was impossible for the human will to be in a true state of total indifference to the different physically possible courses of action and arrive at a decision.28 In this sense, the actions of the human will were necessary, but because they were not subject to the mechanical necessity of the physical world, Wolff said, they were also free.29 Wolff’s rationale failed to impress Lange. In his Modest disquisition of the new system of philosophy of God, the world and man (1723) he wrote that ‘the liberty of free agents . . . must not be confused with spontaneity, which pertains even to brutes and to automata and causes acting from natural necessity’.30 In another work he described spontaneity as no more than ‘an ape and an image of liberty’.31 26

Bianco (1989), p. 111. Thomasius (1994), Lib. I, cap. I, x 54; Lange (1999b), ‘Die erste Stelle’, p. 2. 28 Wolff (1983), p. 250. 29 Bianco (1989), p. 123. 30 ‘[L]ibertas agentium liberorum . . . non confundenda est cum spontaneitate, quae etaim brutis, et automatis caussisque ex necessitate naturae agentibus competit’ (quoted in Bianco, 1989, p. 123). 31 ‘[T]antum simia et simulacrum libertatis’ (quoted in Bianco, 1989, p. 123). 27

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Lange also criticized the Leibnizians’ and Wolffians’ belief that there was only a difference in degree between human and divine rationality and argued that they gave insufficient consideration to God’s active preservation and government of the world.32 Although Lange’s argument therefore seems similar to Clarke’s in many respects, it is not specifically Newtonian and neither Newton nor Clarke play any role in his critique of Wolff. Lange’s interest in affirming the freedom of the will reflected his Pietist concern for spiritual rebirth. If such a spiritual rebirth was to be possible and the teachings of Pietist theologians like Lange on rebirth were to have any purpose at all, then the voluntary reform of the soul had to be possible too, and had to be reflected in a reform of the conduct of life. His emphasis on the active government of the world by God was not related to a Newtonian natural philosophy, but to his belief that God directly punished sinners for their transgressions.33 Another important critic of the pre-established harmony was the physician Georg Ernst Stahl, (1659–1734) also at the University of Halle and author of the Theoria medica of 1708. Stahl’s critique of Leibnizian harmonia praestabilita predated the Leibniz–Clarke correspondence and his natural philosophy differed markedly from that of Newton. Stahl’s medical theory was based on an idea of organism, which was distinct from mechanism. Stahl did not believe that the human soul acted on the physical body in a mechanical fashion, but that the physical body itself was not a purely material entity. The physical body was ensouled, that is, every part of it was permeated by spiritual being. Stahl rejected the idea of a dualism of mind and body and therefore also did not accept the harmonia praestabilita, which was predicated on the dualism of mind and body. Stahl argued that the motions of the physical body could not be explained by the mechanical interaction of inert pieces of matter, but only with the purposive action of a spiritual principle, from which the human body was inseparable.34 Stahl too was concerned to show that the soul’s actions were not necessary in the Leibnizian or Wolffian sense, because Stahl wanted to emphasize the possibility of spiritual regeneration. If the soul’s development was predetermined, however, there was little point in striving for spiritual regeneration. Although therefore Lange, Stahl and other German philosophers might have shared Newton’s and Clarke’s opposition to Leibnizian and Wolffian natural religion and metaphysics and argued in similar ways, they did not draw on Newton or Clarke, let alone Newtonian natural philosophy, but used Thomasian and Pietist currents of thought. The second reason for the reluctance to use Newton or Clarke in debates over metaphysics or natural religion was the general belief that Newton’s achievements were in mathematics and the mathematical description of natural phenomena. Newton, it was often argued, had never intended to treat metaphysical questions. 32

Lange (1999a), ‘Die achte Vorstellung’, p. 91. Ibid., p. 102. 34 See Georg Stahl’s ‘Disquisitio de Organismi et Mechanismi Diversitate’, in Stahl (1737). See also Geyer-Kordesch (2000), p. 160. 33

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The use of Newton as an authority in metaphysics was blamed on Newton’s overzealous followers. It was they who had tried to turn Newtonianism into a general philosophical system, against Newton’s own wishes. This historical argument of limiting Newton’s status to that of a mathematician and natural philosopher was very effective in excluding any form of Newtonian philosophy from German metaphysics. This was so in particular, because one point on which Wolffians and their opponents agreed was that mathematical principles could not be applied to the solution of metaphysical questions. In 1741, for example, Professor Ludwig Kahle, dean of the philosophical faculty of Go¨ttingen University published a critique of Voltaire’s essay on the metaphysics of Newton and Leibniz.35 In the Preface to this work Kahle wrote that Voltaire had claimed to have found a system of metaphysics in Newton’s works. However, it was a mistake to treat Newton as a metaphysician. He had never intended to be one, but had remained content with mathematics and physics. After all, Kahle conceded generously, ‘Newton remains a great man, even if he was no metaphysician’,36 but Newton’s metaphysics were no more than an invention of Voltaire. In his Critical history of philosophy (Historia critica philosophiae) Johann Jacob Brucker in 1744 seconded Kahle’s opinion that Newton had never wanted to formulate a system of metaphysics. Brucker praised Newton as a mathematician and natural philosopher: But hardly ever has there lived a philosopher and mathematician, whom opinion in his lifetime raised to the heavens in the esteem of most people and caused not only to be regarded with astonishment by his own countrymen, but to be admired abroad as well.37 Newtonian metaphysics, however, were an invention of Newton’s followers, which Newton would not have approved, had he known of it. Newtonianism had become a philosophical sect in Britain and it was the members of this sect who ‘placed the great man in the highest place not only among the geometricians, mechanics, astronomers and physicists, but among metaphysicians, too’.38 What led these philosophers to postulate a Newtonian metaphysics was a blind and exaggerated veneration for the undoubtedly remarkable achievements of Sir Isaac. Voltaire had also ‘formulated a Newtonian philosophy’,39 which included a metaphysics and 35 Kahle (1741); Voltaire (1740). The German translation of 1741 was intended as a response to Kahle, as the translator explained (Voltaire, 1741, ‘Vorrede des Uebersetzers’). 36 ‘Neuton bleibt ja deshalb auch groß, wenn er gleich kein Metaphysicus gewesen ist’ (Kahle, 1741, ‘Vorrede’). 37 ‘Vixit autem vix unquam philosophus et mathematicus, quem vivum adhuc adeo doctrina in coelum apud plerosque extulerit, et non civibus modo suis stupendum, sed et exteris admirandum fecerit’ (Brucker, 1744, p. 643). 38 ‘[M]agnum virum non tantum inter geometras, mechanicos, astronomos, physicos, sed inter metaphysicos quoque summo loco ponunt, ne quid sectae suae desit, in quo cum contemtu aliorum gloriari possit’ (Brucker, 1744, p. 646). 39 ‘[P]hilosophiam Newtonianam exsculpsit’ (Brucker, 1744, p. 644).

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natural religion. But all this had occurred ‘had he been alive, against the will of Newton’,40 who ‘while he did not hold metaphysics in contempt, neglected all manner of metaphysical reasoning, as he rejected all hypotheses and took refuge in experience alone’.41 Another historian of philosophy, the Wolffian Jacob Gu¨nther Ludovici, in the 1730s also argued that Newton’s achievements were in mathematics and natural philosophy but not in metaphysics. Newtonian metaphysics was the brainchild of Newton’s disciples, such as Clarke, who attempted to produce a Newtonian metaphysics, ‘although it is well known, that Mr Newton only acquired immortal glory in mathematics, but in the main doctrine fell far short of the achievements of Mr Leibniz’.42 The author of the article on ‘Newtonische Philosophie’ in Zedlers Universallexikon made a similar point in 1740. Henry Pemberton’s system of Newtonian philosophy did Newton a disservice, ‘given how impassioned his [that is, Newton’s] followers are in wanting to turn this geometer into the discoverer of the new true philosophy’. In England Newton enjoyed authority as a philosopher, outside England only as a mathematician.43 Wolffians as much as their critics were convinced that mathematical principles were not transferable to metaphysics or any other parts of philosophy. In the 1741 edition of his Elementa matheseos universae Wolff himself warned of the precipitate application of mathematics to broader philosophical problems by Newtonians: If only those would pay serious attention to this, who from the mathematical principles of natural philosophy and from the optics of the supreme mathematician ISAAC NEWTON try to formulate I do not know what sort of Newtonian philosophy; as if imaginary notions, which are sufficient for the mathematical understanding of nature and are seen to be very fertile there, could be usefully introduced into first philosophy and natural philosophy, even, as if from these imaginary notions conclusions could be drawn concerning natural theology and general cosmology.44 40

‘[I]nvito, si viveret, Newtono’ (ibid). ‘[M]etaphysicam si non plane contemsit, omnem tamen eius ratiocinandi modum neglexit, omnes hypotheses reiiciens, et ad experientiam solam confugiens’ (ibid., p. 646). 42 ‘[O]hnerachtet bekannt genug ist, daß Hr. Neuton bloß in der Mathematick sich einen unsterblichen Ruhm erworben habe; in der Haupt-Lehre aber Hrn. Leibnitzen bey weiten nicht gleich komme’ (Ludovici, 1737, x208). 43 ‘[S]o hat Pemberton dem Herrn Newton bey Verstaendigen einen schlechten Dienst gethan, indem man siehet, wie passionirt die Anha¨nger desselben sind, indem sie diesen Geometram zum Urheber einer neuen und der wahren Philosophie machem wollen’ (Zedler, 1732–1764, ‘Newtonische Philosophie’, col. 414). 44 ‘Utinam huc animum serio adverterent, qui ex Principiis Philosophiae Naturalis Mathematicis & optica mathematici summi ISAACI NEWTONI, nescio quam philosophiam Newtonianam exsculpere volunt, quasi notiones imaginariae, quae ad cognitionem naturae mathematicam sufficiunt, & in ea foecundae deprehenduntur, in Philosophiam primam & naturalem utiliter inveherentur, immo quasi ex istis notionibus imaginariis inferri possent quae ad Theologiam Naturalem & Cosmologiam generalem spectant’ (Wolff, 1971, p. 475.). 41

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The reason Wolff and his followers objected to the use of mathematical principles in metaphysics and other areas of philosophy was that although mathematics might be useful to describe certain phenomena, it did not explain them, because the causes of phenomena such as gravitation were not mathematical. The fact that a particular mathematical formula could be used to predict the speed of a falling object did not mean that the object fell because of this mathematical regularity. ‘For the sake of mathematical understanding much can be invented, but these mathematical fictions are not themselves the true causes, by which the effects of Nature are explained in an intelligible fashion’.45 Kahle later cited this passage approvingly in his refutation of Voltaire.46 Anti-Wolffian philosophers were at least equally hostile to the use of mathematics in metaphysics, often arguing that the Wolffians themselves had committed this mistake. Newton’s reputation of being mainly a mathematician did anything but encourage critics of Wolff to appeal to Newton’s authority in debates over metaphysics. One example of such a critic of Wolff is Johann Gottfried Walther (1684– 1748) who published a work entitled Eleatic graves opened or a careful examination of the Wolffian and Leibnizian foundations of philosophy.47 The title was a reference to the ancient Greek Eleatics’ contempt for sensory perception and their emphasis on pure thought alone as a means to examining the divine hen kai pan, an idea, which Walther believed had been revived by Leibniz and Wolff. Walther opposes a characteristically Pietist and Thomasian interest in the reformation of will to Wolff’s stress on the intellect.48 In the course of his argument Walther once refers to Newton, but this is only as an example of the use of mathematics in mechanics, not of Newton’s importance as a metaphysician or natural theologian. As Walther writes, ‘Algebra has so far, by the efforts of great scholars, produced astonishing results in mechanics, the doctrines of the movements of heavenly bodies etc., as is evident from the fruits of the diligence of Mr Newton and others’, but he does not believe these mathematical achievements to have any relevance for metaphysics.49 At the university of Jena the philosopher Johannes Buddeus published a condemnation of Wolff’s philosophy, in which he claimed that mathematics was the cause of the main Wolffian errors, particularly the denial of a free will.50 Joachim Lange also believed that ‘metaphysical truths are of a completely different kind from mathematical truths’ and that Leibniz and Wolff had ignored this distinction.51 The same criticism appeared in the work of Johann Heinrich Gottlob Justi, the 45 ‘In usum cognitionis mathematicae multa fingere licet, sed fictiones istae mathematicae non sunt verae caussae, quibus effectus Naturae intelligibili modo explicantur’ (ibid). 46 Kahle (1741), p. 159. 47 Walther (1724). 48 See the ‘Vorrede’ in Walther (1724). 49 ‘Die Algebre hat bißher, durch Bemu¨hung grosser Gelehrten, in der mechanic, in denen Lehren von Bewegung der himmlischen Co¨rper etc. erstaunende Proben gethan, wie davon Mr. Nevvton und andere uns die Fru¨chte ihres Fleisses vor die Augen geleget’ (Walther, 1724, Ch. 10). 50 Israel (2001), p. 546. 51 ‘[D]aß die metaphysischen Wahrheiten von einer gantz anderen Beschaffenheit sind, als die mathematischen’ (Lange, 1999a, ‘Die erste Vorstellung, p. 9).

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winner of the Berlin Academy prize for his essay on monads, published in 1748. Mathematics, he wrote, must not be mixed with metaphysics.52 While Newton in Germany never gained recognition as a metaphysician, this does not mean that no Newtonian doctrines found acceptance. Newton’s optics, unlike his physics, were largely compatible with Wolff’s philosophy and Wolff himself could praise Newton for discussing ‘in his outstanding work on optics new properties of light, which had not been noticed before’.53 G. F. Richter also defended Newtonian optics against the Italian Giovanni Rizzetti.54 But not only were Newton’s views in areas outside mathematics and optics more contentious. The general meaning of ‘Newtonianism’ or ‘Newtonian philosophy’ itself was also limited to a collection of specific mathematical and natural philosophical theories. These were not related to a comprehensive, specifically Newtonian philosophical system, because a system of this kind, it was argued, did not exist. The article on ‘Newtonische Philosophie’ in the main encyclopedia of mid-eighteenth century Germany, Zedler’s Universallexikon, for example, was an unconnected list of contemporary debates on specific mathematical and natural philosophical questions. The 1740s have often been seen as a turning-point in the reception of Newtonianism in Germany. Although Wolff was rehabilitated by King Frederick William of Prussia in 1736,55 in the following years the influence of Wolffian philosophy declined to a certain extent, at least in Prussia. Frederick II was not sympathetic to Wolffian metaphysics.56 Among the philosophers he cultivated were numerous anti-Wolffians, many of them foreigners, such as Voltaire, d’Argens, Algarotti or Maupertuis. When Frederick revived the Royal Academy of the Sciences in Berlin in 1743 he did offer a post to Wolff, who, however, preferred to return to Halle.57 In 1746 Maupertuis became president of the Berlin Academy,58 and Leonhard Euler (1707–1783), the Swiss mathematician, also held a post at the Academy from 1741 to 1766. Euler was described by at least one eighteenth-century German philosopher as a Newtonian59 and in more recent secondary literature it has been said that ‘Maupertuis and Euler established Newtonian theory in Prussia’.60 The Berlin Academy, it has been argued, was split between a faction of Franco-Swiss Newtonians, such as Euler and Maupertuis, and a group of Wolffians.61 There are, 52

Justi (1748a). ‘Vir summus Newtonus in egregio optices opere novas luminis proprietates, ante nondum animadversas . . . per experimentum edocet’ (Wolff, 1971, p. 97). 54 Richter (1724). 55 Bianco (1989), p. 110. 56 Blanning (1997), p. 544. 57 McClellan (1985), p. 77. 58 Clark (1999), p. 439. 59 Eberhard (1796), p. 303–304, where Euler is listed as one of only two Newtonians in Switzerland and Germany. 60 Calinger (1969), p. 319, though Calinger himself qualifies this characterization of Euler as a Newtonian towards the end of the same article. 61 Israel (2001), p. 557. 53

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however, several reasons for qualifying this characterization of Euler and his colleagues at the Berlin Academy as representatives of a new ‘Newtonianism’ in Prussia.

4. Newtonianism and the critique of dogmatic philosophy in the Berlin Academy As the writings of Lange or Stahl illustrate, there was a strong dissatisfaction with Leibnizian and Wolffian philosophy already in the first four decades of the eighteenth century, independently of Newtonian ideas. At times, recognizably Newtonian arguments did make an appearance in the critiques of Wolffian philosophy in the 1740s. In general, however, the adoption of Newtonian arguments was irregular, eclectic and piecemeal. Moreover, it is not only true that the ideas of ‘Newtonians’ differed from those of Newton himself.62 So-called ‘Newtonians’, such as Euler, it seems, were also reluctant to describe themselves as such and did not consider their natural philosophy to be ‘Newtonian’. Although they sided with Newton on particular questions, this did not necessarily mean that they were members of a Newtonian school. Adopting a label of ‘Newtonianism’, it seems, would have suggested that they were guided by a dogmatic belief in Newton’s authority rather than a desire for truth. It was this sort of philosophical dogmatism which Brucker, for example, had criticized in British Newtonians, who, he said, were led by veneration for Sir Isaac rather than independent thinking.63 There were important grounds for dissatisfaction with Wolffian philosophy, mainly because of its Spinozist implications for human free will, which Euler and many others before him had singled out for criticism. But the aim of the anti-Wolffians was only to oppose a coherent philosophical system to Wolffianism, not to replace it with an explicitly Newtonian equivalent. The work of Euler himself illustrates the limited extent to which it is possible to speak of a turn towards Newtonianism at the Berlin Academy. Euler differed from earlier critics of Wolff active in Germany in that he placed much greater emphasis on a theory of physics. In the works of philosophers such as Lange or even Stahl the natural philosophical foundation of their critique of Wolff was much less sophisticated or prominent. The concept of physical inertia also fulfilled an important function in Euler’s critique. To this extent Euler could be seen to be a Newtonian, but the examination of other parts of his scientific work will show that Euler’s reception of Newton’s ideas was also highly selective and that the description of Euler as a ‘Newtonian’ is true only to a rather limited degree. This is so, especially if one turns to Euler’s own understanding of his natural philosophy. In 1746 an important critique of the theory of monads was published anonymously by Euler as Thoughts on the elements of corporeal entities, in which the doctrinal system of the simple beings and monads is examined, and the true nature of 62 63

Fara (2002), p. 115. Brucker (1744), p. 646.

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corporeal entities is discovered.64 After summarizing the theory of monads in the first part of this essay, Euler put forward his critique of monadology in the second. Euler argued that the first law of motion was that every corporeal entity persisted in its condition, unless something acted on it from the outside. This was the vis inertiae and was a general property of bodies, like extension. Inertia was a force to resist change from the outside, because if ‘a body would accommodate itself to all changes, without resisting it in the least, one could not say that it was endowed with a force to persist in its condition’.65 Unlike Wolff, Euler did not believe that extended bodies had an internal principle of change. Changes in the states of extended bodies were the result of external action by other bodies, which the bodies acted upon resisted with their vis inertiae. If bodies had no power to resist other extended bodies then each extended body would forever persist in the same state of motion from creation. The origin of change in the world, therefore, was the vis inertiae, on which the ability of one body to resist the motion of another rested. Euler’s critique also extended to Wolff’s theory of the soul. Wolff conceived of souls as monads, which had their own internal necessary principles of change, like physical bodies. Euler rejected both the argument that the physical elements and souls were of one kind and the belief that the changes in souls were the result of necessary internal principles of change. He argued that physical bodies and spirits or souls were different in essence. The former were entia passiva, while souls were entia activa.66 Souls also were free in their actions. This freedom was as much an essential property of souls as extension and vis inertiae were essential properties of extended bodies.67 Euler’s critique of the monadology therefore was relevant to the question of human free will, a question he discussed in greater detail in his later Letters to a German Princess (1768–1772).68 Euler’s position could be characterized as Newtonian in a loose sense in that a vis inertiae plays an important role in his physics and in his critique of Wolff’s conception of extended bodies and souls. Euler also praised Newton for discovering universal gravitation.69 But in other respects Euler was not a Newtonian. His mathematical methods were not Newtonian, as Guicciardini has emphasized.70 Moreover, in spite of his admiration for Newton it is also clear that Euler did not see himself as a member of a Newtonian school. In the Letters to a German Princess Euler criticized Newton’s theory of sunlight as beams emanating from the sun and travelling through a void between the sun 64

Euler (1942). ‘Denn wann ein Ko¨rper sich zu allen Vera¨nderungen, ohne derselben sich im geringsten zu wiedersetzen, bequemen sollte, so ko¨nnte man auch nicht sagen, dass derselbe mit einer Kraft in seinem Zustande zu verharren begabet wa¨re’ (Euler, 1942, p. 355). 66 Ibid., p. 361. 67 Ibid. 68 Euler (1986), 85. Brief, p. 22. 69 Ibid., 52. Brief, p. 182. 70 Guicciardini (1999), p. 6. Guicciardini writes that ‘[a]fter Euler the Principia’s mathematical methods belong definitely to what is past and obsolete’. 65

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and the earth. In that case, Euler argued, the rays of light from the sun would have to travel at an incredible speed and would collide with rays of light from other stars. Euler instead preferred Descartes’s explanation of sunlight as vibrations transmitted from sun to earth through an intermediate ether.71 Euler also contradicted Newton’s belief that objects which did not shine with their own light were visible only because of the light they reflected from other sources. Euler argues that this is clear from the fact that the view in a mirror, which does reflect rays of light, changes as the position of the observer changes, while this is not true for ‘dark objects’ (dunkle Koerper). Euler suggests instead that light causes the particles on the surface of these dark objects to vibrate. These vibrations are transmitted to the ether between the object and the observer and are perceived by the eye as colours. Different colours are the result of different rates of vibration in the particles on the surface of these dark bodies.72 The conclusion Euler draws from his criticism of Newton’s theories is that even as great a mind as Newton could err and that this should inspire everybody else to modesty.73 More important than the authority of a great figure, it seems, was intellectual modesty and the willingness to abandon previous beliefs, if they were proved false. Being categorized as a Newtonian would probably have implied to Euler that he formed his opinions dogmatically, on the basis of a blind belief in Newton’s authority. It is also evident from other sources that criticism of Wolff in the Berlin Academy did not automatically imply the presence of Newtonianism. In 1747 the Berlin Academy offered a prize for the best essay on monadology. Monads had been the subject of increasing controversy for some time. Euler’s essay of 1746 drew several anonymous replies in defence of monadology.74 Euler later observed that in that year: the dispute about monads was so lively and general that one spoke of them heatedly in all companies, even in the corps-de-garde. There was almost not a single lady at court who had not declared herself for or against monads. Everyone’s conversation fell upon monads everywhere and no one spoke of anything else.75 When the Berlin Academy came to determine the winner of the prize for the best essay on monadology, the question had become so heated that all four classes of the academy were involved in determining the winner, although the question had been posed only by the philosophical class. The participation of the other classes 71

Euler (1986), 17. Brief and 18. Brief. Ibid., 27. Brief. 73 Ibid., 24. Brief, p. 82: ‘Ueberhaupt schuetzet nicht immer die Groeße des Geistes vor der Ungereimtheit der Meynungen, die man einmal angenommen hat’. For a similar comment see ibid., 18. Brief, p. 60. 74 Clark (1999), p. 440. 75 Ibid., p. 440. 72

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helped Euler to rig the decision: the prize was awarded to an essay against monads, written by Johann Gottlob Justi, a councillor (Rath) from Eisenach.76 Justi’s entry for the Berlin Academy’s prize was no example of Newtonianism. Towards the end of his essay, for example, he rejected Newtonian vis inertiae as a natural philosophical concept, apparently misunderstanding it.77 Throughout a large part of the essay he concentrates on the question of the divisibility of matter, in a manner which is similar to Euler’s argument in the Gedancken.78 The belief that there are simple elements, monads, of which all corporeal entities consist, is based on the idea that matter cannot be infinitely divisible. The defenders of monads argue that monads are simple elements without extension, because they are not divisible, and that they are endowed with motive force. Justi, however, said that matter was infinitely divisible. There could be no simple elements without spatial extension, because however many of these simple elements or monads were added to each other, they could never form an extended body if they themselves were not extended.79 Also, if matter consisted of unextended simple elements, it would be possible for humans to destroy matter by dividing it until it was reduced to these simple elements and ceased to be matter because it was no longer spatially extended. The power of annihilating matter, however, had to be reserved for God.80 Like Lange before him, Justi also criticized Wolff for transferring mathematical concepts to metaphysics and for over-estimating the powers of human reason in examining the grounds of God’s actions. These remained largely inscrutable to humans.81 There is also little sign of a clear-cut Newtonianism among other critics of monads, such as the clergyman Georg Wilhelm Wegner. Wegner’s critique was published by the Berlin Academy together with Justi’s essay. Wegner, like Justi, focuses on the divisibility of matter. Unlike Justi, he argues that all extended bodies consist of simple elements, which are indivisible by natural means. But although these elements cannot be subdivided further by natural means, they are nevertheless extended in space and could be divided into smaller elements by God.82 Wegner thereby circumvents the problem that simple elements had to be either extended in space, and therefore divisible into further smaller elements, or not extended at all, and therefore incapable of forming extended bodies, however many of them are aggregated. Like Euler and Justi, Wegner emphasizes the limits of human reason in understanding the composition and substance of natural bodies: 76 77 78 79 80 81 82

Ibid., p. 440. Justi (1748a), x LXXIX. Euler (1942), x71, p. 364. Justi (1748a), x XLIX. Ibid., x XXXVIII. See ibid., x XXIV and x XXXVII; Justi (1748b), ‘Erste Abtheilung’, especially xx 45, 66 and 67. Wegner (1748), p. 12.

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Given the infinite divisibility of matter it is not at all surprising, that a finite understanding is not capable of understanding fully those matters, which tend towards the infinite. I therefore conclude with the motto of the famous Heinsius, which I also elect as my own maxim, How much it is that we do not know.83 Wegner did not appeal to Newton’s authority, since Newtonian ideas were irrelevant to his argument. Wegner wrote, for example, that there was no vis inertiae in the proper sense and that the gravity of bodies is the result of a separate type of matter, ‘which is called the heavy-making’.84 Of the dissertations on monads printed by the Berlin Academy, the most Newtonian was probably the second, ‘De elementis’, in which the anonymous author put forward a corpuscular natural philosophy and defended Newton’s theory of gravity against Descartes and Huygens.85 In another essay printed by the Academy Newton again was criticized for his lack of metaphysical depth: ‘Newton studied physics zealously, metaphysics only incidentally: why therefore is it surprising to find that this immortal man of immense merit erred in those matters, in which he wished to be an outsider?’86 In general, however, there is no clear-cut division between Newtonians and Wolffians in the disputes over monads. The opponents of Wolff did not present themselves as ‘Newtonians’. It was only in the two decades after about 1750 that Newtonianism apparently became more fashionable and began to be used as a label for a more comprehensive philosophical system or method. Central to this development was Newton’s reputation as a non-metaphysical philosopher. Although this had been a reason for denying the existence of a Newtonian system or method altogether before, the lack of metaphysical subtlety now came to be seen as one of its main benefits.

5. Conclusion: Newtonianism and the German Enlightenment after the 1750s From the second half of the eighteenth century Leibnizian–Wolffian metaphysics increasingly fell into disrepute.87 It was criticized for its excessive emphasis on a priori reasoning, its obscurity and its neglect of sensory experience. In these circumstances it seems to be precisely Newton’s well-established reputation as a nonmetaphysical philosopher and empiricist, which explains much of his growth in popularity. Until then Newton’s ‘modesty’, that is, his alleged reluctance to focus on anything but sense experience and to enter into metaphysical speculation had 83 ‘Bey der unendlichen Theilbarkeit der Materie ist es am allerwenigsten zu verwundern, da ein endlicher Verstand Dinge, die ins unendliche hinaus laufen, vo¨llig zu begreiffen nicht im Stande ist. Ich schliesse demnach mit dem Symbolo des beru¨hmten Heinsius, welches ich auch zu meiner Devise erwa¨hle: Quantum est quod nescimus’ (Wegner, 1748, p. 64). 84 ‘[W]elche man die schwermachende nennt’ (Wegner, 1748, p. 16). 85 Anon. (1748a), xXVI, p. 21 and xXXVII, p. 30. 86 ‘Neutonus studio Physicum incidenter Metaphysicum egit: quid ergo mirandum, virum ingenti merito immortalem in iis errasse, quorum se voluit esse hospitem?’ (Anon., 1748b, xIII, p. 42). 87 Beiser (1987), p. 4.

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been considered a philosophical defect, if it was commented on at all. At best, it was seen as an example of laudable restraint in someone who was not a competent metaphysician, but it was not argued that Newtonianism represented a fruitful philosophical method precisely because it was not a form of speculative metaphysics. Although there were critics of Wolffian metaphysics before the mid-eighteenth century, these did not appeal to Newtonianism as an alternative to Wolffianism. This seems to have changed from the 1770s, especially. ‘Newtonian method’, which was only loosely related to Newton’s original ideas, came to be regarded as a remedy against the problems of Leibnizian and Wolffian quasi-scholastic metaphysics. One indication of this trend are the numerous translations from English of works popularizing Newtonianism, particularly from the 1770s: a German translation of Benjamin Martin’s Philosophia Britannica appeared in 1778 and several works by James Ferguson were published in German in the 1770s and 1780s.88 In his Preface to the Philosophia Britannica the translator Christian Wilke emphasized the importance of abandoning ‘all metaphysical rarities, such as that of a best world, simple things, a predetermined harmony and other such verbal inanities’, which had originated with Leibniz. On this basis the English had constructed their so-called Philosophia Britannica, that is Newtonianism.89 There were also German philosophers who claimed to be following a Newtonian method in their philosophy. One of the most interesting examples of this comes from a Jesuit, Jacob Zallinger. In the Preface to The interpretation of nature, or philosophy put forward by a Newtonian method he declared his commitment to a ‘Newtonian’ method and defined it in the following manner: Having rejected hypotheses and arbitrary notions and having left aside that anxious desire to fabricate systems, which refer to the universal nature of things, famous men took on the task of interpreting nature by contemplating its works and, as it were, listening to its voice. And this is the very method, which is named the NEWTONIAN, after NEWTON, that incomparable man of immortal memory.90 This did not mean that he ‘considered all sayings by Newton to be oracles’ or that he believed all theories of other philosophers to be redundant. But he believed that Newtonianism as a style or manner of philosophizing was to be preferred to all 88

Martin (1778); Ferguson (1771); Ferguson (1783); Kirchhof (1781). ‘[A]lle metaphysische Rarita¨ten, wie z.B. von einer besten Welt, einfachen Dingen, vorbestimmten ¨ bersetzers’, p. XXXIV). Harmonie, Wortkra¨mereyen u. dergl. verlassen’ (Martin, 1778, ‘Vorbericht des U The fact that ‘Newtonianism’ in these popularizing works was presented without complex mathematical argument also helped their acceptance. 90 ‘[R]eiectis hypothesibus quae ad universam rerum naturam pertinerent, cura praetermissa, id egere viri praeclari, ut opera naturae contemplantes, eiusque veluti vocem audientes, eandem sibi interpretandum sumerent. Atque haec est ipsa methodus, quam a NEWTONO incomparabili viro, & immortalis memoriae, NEWTONIANAM vocant’ (Zallinger, 1773, Vol. 1, ‘Praefatio’). 89

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others.91 Although therefore Wilke or Zallinger were not intending to adopt Newton’s views on everything, they themselves described their philosophy as ‘Newtonian’. Their ‘Newtonianism’ was a sort of philosophical eclecticism, opposed to the over-systematization and speculative dogmatism of Wolffian metaphysicians.92 Newton’s reputation, reflected in writings by philosophers such as Zallinger, was now that of an undogmatic philosopher, who refused rather than failed to enter into metaphysical speculation. At the same time, the older belief that ‘Newtonianism’ was based on a blind, dogmatic faith in Newton’s philosophical authority also continued to be held by some. In his Farbenlehre (1810) Goethe, for example, criticized Newtonian optics as a dogmatic system, similar to the Roman Catholic Church, and compared his own attempts at natural philosophy to Luther’s reformation of faith.93 The original historical argument that Newton had never intended to treat of metaphysics could, therefore, be developed in two ways. It could be interpreted in a positive sense as proof that Newton had successfully avoided senseless metaphysical speculation. Or, it could be understood as evidence that a ‘Newtonian philosophy, which required a metaphysics, was not Newton’s creation, but that of self-declared followers, who dogmatically adopted Newton as their infallible guide to all philosophical questions. The assumptions on which both views, that of Newtonianism as a corrective of metaphysical subtlety and that of Newtonianism as a form of dogmatic philosophy, were based had been formed in Germany in the course of the three decades after the German publication of the Leibniz–Clarke correspondence in 1720.

Acknowledgements I am grateful to Professor Ludmilla Jordanova and Mr Scott Mandelbrote for comments on an earlier draft of this article.

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