Locke's Essay and Newton's PrincipiaAuthor(s): G. A. J. RogersSource: Journal of the History of Ideas, Vol. 39, No. 2 (Apr. - Jun., 1978), pp. 217-232Published by: University of Pennsylvania PressStable URL: http://www.jstor.org/stable/2708776 .Accessed: 08/03/2011 19:39

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LOCKE'S ESSAY AND NEWTON'S PRINCIPIA

BY G. A. J. ROGERS*

I. Introduction.

There is a standard picture of the relationship between John Locke and Isaac Newton which might be expressed in the following way: Locke's intellectual and philosophical attitude was molded by what he saw in the Newtonian achievement and was largely responsible for the general tone and nature of Locke's philosophical position. According to this view in the interaction between the two men Locke was the indebted

partner, learning much from his younger colleague, whilst Newton learnt little, if anything, from the older man. It is indeed sometimes claimed (see below) that Newton's Principia completely changed Locke's intel- lectual stance, whilst Newton, it is assumed, was not greatly influenced by Locke at all. Such opinions of the relation between Locke and Newton are to be found amongst historians of science especially, though philosophers too, writing on the history of their subject, have sometimes been inclined to see the influence of Newton as very substantial. There are many passages in commentaries on Locke and Newton which reveal this attitude but I shall draw attention to only four, though all are recent and reflect positions held by respected scholars. The first is taken from the notes to Newton's Correspondence, Volume III, by H. W. Turn- bull. Of Locke, Turnbull wrote: "John Locke (1632-1704), philosopher, ... He became a friend of Newton through reading the Principia and he early introduced its philosophical principles into his writings. . . ." The implication is clearly that there were specific Newtonian influences to be found in Locke's work and that these influences were considerable. The second example is taken from a broadcast discussion on Newton's Principia between I. Bernard Cohen and Peter Laslett. Locke, Laslett rightly said, read the Principia just after he had written the Essay Con- cerning Human Understanding. Laslett went on:

Locke, then, had written a traditional philosopher's review of the world and was preparing it for the press when he was suddenly faced with this astonish- ing book of the greatest intellect amongst his contemporaries and convinced that he didn't understand the natural world at all. The result was, in my view,

* Support for research in connection with this paper was provided by a grant from the Royal Society. I am very grateful to the following for their comments on earlier versions of this paper: R. I. Aaron, A Rupert Hall, John Harrison, Peter Laslett, D. T. Whiteside, and J. W. Yolton.

1 The Correspondence of Isaac Newton (Cambridge, 1959-), Vol. III, edited by H. W. Turnbull, and J. F. Scott, 76.

217

218 G. A. J. ROGERS

that he wrote the very remarkable epistle to the reader in the Essay on Human Understanding, in which he says: "I am only an under-labourer. Newton, Huygens, are those who really understand the world. My function is to clear away the rubbish. This is a complete revisal of the social and the intellectual position of the philosopher. And this could be said to be historically the beginning of the two cultures .. ."2

We shall turn later to a more detailed look at Laslett's statement. For the moment, let us just note that once again we have the view expressed that the Principia had a very substantial influence on Locke's philosophy. Once again there is no suggestion that Locke's philosophy had any influ- ence on Newton. This general position is summarized by A. R. and M. B. Hall: Newton, they write, "is commonly regarded as furnishing the scientific substratum of Locke's philosophy."3 It is a view from which the authors do not dissent. My fourth example is taken from John Herman Randall's The Career of Philosophy:

Locke's Essay stands with Newton's Principia as the fountainhead of British and French thought in the eighteenth century, as a classic illustration of the application of the Newtonian "geometrical" or "analytical" method to human nature.4 . . . In point of fact, Locke assumed to begin with and without

question the whole of Newtonian science, both its verdict on the nature of science and on the nature of the world.5

This paper challenges that standard view of the interaction between the two men. I show first that the influence of Newton on Locke was not

nearly as straightforward or as great as it is often depicted.5 Second, I shall argue that there was some mutual influence, and suggest that Locke's philosophy may have had a positive influence over Newton's own thought.6 From this there emerges a new perspective on a crucial

2 Published in The Listener (9 December, 1971), 792. 3 A. R. Hall and Marie Boas Hall, Unpublished Scientific Papers of Isaac

Newton (Cambridge, 1962), 81. 4 John Herman Randall, Jr., The Career of Philosophy. Vol. I. From the Middle

Ages to the Enlightenment (New York and London, 1962), 595. 5 Ibid., 601. 5a In a second, and subsequent papers, I shall argue that there was some mutual

influence, and suggest that Locke's philosophy may have had a positive influence on Newton's own thought.

6 Recently James L. Axtell has done much to set the record straight and to add to our knowledge of the interaction between Locke and Newton. His papers on this are: "Locke, Newton, and the Elements of Natural Philosophy," Paeda-

gogica Europae, I (1965), 235-45; "Locke's Review of the Principia," Notes and Records of the Royal Society of London, 20 (1965), 152-61; "Locke, Newton and The Two Cultures," John Locke: Problems and Perspectives (Cambridge, 1969); also the introduction to Axtell's edition of Locke's Educational Writings (Cam- bridge, 1968). I do not always share Axtell's conclusions, however. J. E. McGuire in his writings on Newton has also noticed that Locke may well have been an influence upon Newton's thought. Thus, in his "The Origin of Newton's Doctrine of Essential Qualities," Centaurus, 12 (1968), 238-39, McGuire suggests that

LOCKE'S ESSA Y AND NEWTON'S PRINCIPIA 219

period of seventeenth-century thought, namely, that the effect of Locke's philosophy on the acceptability of the new science was probably more profound than is generally recognized.

Locke's most important philosophical work is, of course, his Essay Concerning Human Understanding and if we are to find the influence of Newton in his writings it is there that we should look. To appreciate correctly the influence of Newton on Locke's work it is absolutely vital that we are accurate about the dates when Locke wrote the Essay and also when he read or otherwise came to know of Newton's work. This is especially important because there has been considerable confusion in some people's mind about the relative dates of the two thinkers. First, one general point, which is obvious, but is still sometimes overlooked, is that Locke saw only the first edition of Newton's Principia (1687). Locke died in 1704; the second and third editions were published in 1713 and 1726, and, as is well known, there are considerable important differ- ences between the three. Newton's other classic of science, the Opticks, was published in 1704, shortly before Locke's death, and too late to have any direct influence on Locke, though this is not to say that Locke was not aware of Newton's work in optics, much of which had been published in the Transactions of the Royal Society. It is perhaps sur-

prising, but such elementary facts have been overlooked by writers on Locke, Newton, and the Enlightenment.7

Locke may well have modified Newton's views on the distinction between primary and secondary qualities. See as well McGuire, "Atoms and the 'Analogy of Nature': Newton's Third Rule of Philosophizing," Studies in History and Philosophy of Science, 1 (1970), esp. 32-35.

7 I give three examples where the lack of proper dating has led to either a flat mistake or a wrong emphasis about the connection between Locke and Newton.

Example 1. In his Locke's Theory of Knowledge and its Historical Relations

(Cambridge, 1917, reprinted in 1960) J. Gibson, in discussing Locke's views on

space, wrote: "Since the distinction between 'space in itself', as something 'uniform and boundless', and the extension of body which is presented to us in sense per- ception, can hardly be regarded as the direct product of Locke's own principles, it is natural to look for some external influence to account for the doctrine of the

Essay. Now we know that Locke was a diligent student of the less mathematical

portions of Newton's Principia, which was published in 1686, four years before the Essay. We can hardly, it would seem, be wrong in connecting Locke's recently acquired views about 'space in itself' with Newton's exposition of 'absolute space' . ." (251). But we now know that this distinction was made by Locke as early as 1676. It is to be found in his journal entry for March 27th. This is now pub- lished in An Early Draft of Locke's Essay, Together With Excerpts from his

Journals, edited by R. I. Aaron and Jocelyn Gibb (Oxford, 1936), 77. Gibson assumed that Locke had read the Principia when he wrote Essay, II, 15, but it had not then even been published.

Example 2. In his Isaac Newton (Clarendon Biographies, Oxford, 1967) J. D. North writes: "The Opticks, on the other hand, was tolerably easy reading, and, strangely enough, it was through this work that many had their only first-hand

220 G. A. J. ROGERS

To appreciate the relationship between Locke and Newton, including their mutual influence, we must clearly recognize that each wrote his most important work independently of the other. Of the influence of Locke on the Principia in its first edition there can be no question: we know of none, nor is it likely that any will ever be discovered. But it is not fully appreciated that the first edition of the Essay Concerning Human Under- standing (1690) was almost equally unaffected by the Principia.

Leaving the production of the first edition of the Principia to one side, therefore, as one where there is no problem, let us turn to the writing of the Essay.

II. The Production of the Esgay. There are three drafts of Locke's Essay extant.8 Following Aaron I

shall refer to them as Drafts A, B, and C. Drafts A and B were written in 1671. Draft C was written in 1685. A version very nearly the same as the published edition was completed by December 1686 when Locke sent the fourth book to Edward Clarke who had already received the three earlier books. Locke was then in Holland, where he had been since 1683. He wrote to Clarke on the 31st December:

You have here at length the fourth and last book of my scattered thoughts concerning the Understanding, and I see now more than ever that I have reason to call them scattered, since never having looked them over all together

encounter with Newton's thoughts on gravitation. John Locke, the philosopher, was much influenced by it ..." (24). As we have noted above, the Opticks was not published until just before Locke's death. The ultimate source for North's view is probably the passage from Desaguliers, quoted p. 7. See also note 31 below.

Example 3. Jonathan Bennett, in his Locke, Berkeley, Hume. Central Themes

(Oxford, 1971) writes: "Locke inherited from Descartes, or borrowed from Newton and Boyle, a distinction between 'primary' and 'secondary' qualities" (89). The distinction is made by Locke as early as 1671 (cf. An Early Draft, 73-74). There is no reason to believe that Locke was influenced by Newton at all in his formula- tion of the distinction.

8 The earlier 1671 Draft (Draft A) is in the Houghton Library, Harvard

University. The later 1671 Draft (Draft B) is in the Bodleian Library. The draft of 1685 is in the Pierpont Morgan Library in New York. There is a different ver- sion of the first draft in the Shaftsbury Papers in the Public Record Office. (Cf. Peter Laslett in Mind [Jan. 1952], 89-92.) On all of these drafts see Aaron, John Locke (Third edition, Oxford, 1971), 50-73. Draft A has been published in An

Early Draft of Locke's Essay Together with Excerpts from his Journals, edited by R. I. Aaron and Jocelyn Gibb (Oxford, 1936). Draft B has also been published as An Essay Concerning the Understanding, Knowledge, Opinion, and Assent, edited

by Benjamin Rand (Cambridge, Mass., 1931). Draft C has not yet been published, but is to be included in the forth-coming volume Drafts for An Essay Concerning Human Understanding, edited by Peter H. Nidditch in The Clarendon Edition of the Works of John Locke series.

LOCKE'S ESSAY AND NEWTON'S PRINCIPIA 221

till since this last part was done, I find the ill effects of writing in patches and at distant times as this whole essay has been.9

We do not possess the draft which Clarke received from Locke.1? But Draft C does tell us quite a lot about the composition of the Essay in its later stages even though it is a draft of only the first two books. What it indicates in a very clear way is that on substantial points the published work argued the same position as that put forward by Locke in 1685. There are differences, some of them of considerable interest. But the differences which do exist show no sign at all of the impact on Locke of reading Newton's Principia. The only recognition accorded Newton in the first edition of the Essay is in the famous "Epistle to the Reader" where Locke clearly places Newton as the greatest among contemporary scientists.

That Locke does not accord Newton any other recognition shows that whilst he was revising the Essay for publication Locke was not at all inclined to alter it to take account of the Principia." In no way did Locke feel that Newton's work called into question any parts of his major arguments. Nor can Locke's attitude be explained by either his unfamil- iarity with, or lack of understanding of, the Principia. (Both of these points are taken up below.) If there are any conflicts between what is said in the Essay and what is said in the Principia then it is fairly safe to assume that either Locke did not notice them or he did not believe that they were worth following up. There is in fact only one major point of potential conflict in the two books and that is in the respective treatment each gives to the notions of space and time. Locke never accepted Newton's absolutist position on space.l2 It is a sign of some of the very

9 The Correspondence of John Locke and Edward Clarke, ed. Benjamin Rand (London, 1927), 177.

10 Here I follow Aaron in believing that Draft C as we have it was not the draft which Clarke received from Locke. It is likely that Draft C never reached England. Cf. Aaron, John Locke, 57.

11 We know that Locke was indeed revising the Essay as late as 1689 for that is the date which appears in Essay, II, XIV, 30. The passage reads: "Hence we see that some men imagine the duration of the world from its first existence to this present year 1689 to have been 5639 years .. ." (Quotations from the Essay will either be from the first edition of 1690, as this one is, or from the Everyman edition, edited by John W. Yolton [London, 1961], 2 vols.) Since commencing work on this paper the Clarendon Edition of Locke's Essay, edited by P. H. Nidditch has been published and it has proved an invaluable guide to the Essay and its history. In Draft C Locke had written: "Hence we see that some men imagin ye duration of ye world from its first existence to this present year 1671 to have been 5619 years...." Cf. also Draft B ? 120. It is odd that Locke does not make the right correction to the figure for the duration of the world.

12 Aaron (op. cit., 156f.) has already drawn attention to the fact that it is

wrong to view Locke's account of space as Newtonian, and he rightly places important weight on the discussions of space in the drafts of the Essay and in

222 G. A. J. ROGERS

different intellectual influences on each of them in their formative years. Put simply, Newton was much more strongly influenced by the Cambridge Platonists, and Platonic views generally, than Locke was. Indeed Locke was consistently strongly and overtly hostile to a very great deal of the Platonism that he currently found.13 This difference between the two men and its importance for an understanding of their relationship will be explored below in section VII. One further comment only is in order here. It is that once again it is vital that it is remembered that Locke saw only the first edition of the Principia, for in it the only discussion of absolute space and time is in the Scholium added to Definition VIII. That discussion is comparatively austere. The full metaphysical and theolog- ical implications of Newton's views on space and time were only clearly brought out in the General Scholium of the second edition of 1713. It was Newton's remarks in this section of the Principia which were to be the main source for the exchanges on absolute space and time in the Leibniz-Clarke correspondence of 1715-16. From this we can see that from Locke's reading of the Principia, prior to his completion of his preparation of the Essay for the press, he did not have much evidence from which he might draw the conclusion that a great deal might turn on the differences between his own and Newton's views on space and time.14 What Locke would have undoubtedly gathered from his reading of the Principia was that Newton did not at all subscribe to the view of

Locke's journals. Another potential point of conflict was not apparent from the first edition of the Principia. That was their differing views on the primary- secondary quality distinction. This topic would require a separate paper, but see McGuire's paper cited in Note 6. In the first edition of the Principia Newton does not include what in the second edition was to become Rule III.

13 On this see G. A. J. Rogers, "Locke, Newton, and the Cambridge Platonists on Innate Ideas," JHI (April 1979).

14 In the Scholium to Definition VIII Newton begins: "Hitherto I have laid down the definitions of such words as are less known, and explained the sense in which I would have them to be understood in the following discourse. I do not define time, space, place, and motion, as being well known to all. Only I must observe, that the common people conceive those quantities under no other notions but from the relation they bear to sensible objects. And thence arise certain

prejudices, for the removing of which it will be convenient to distinguish them into absolute and relative, true and apparent, mathematical and common." Mathematical Principles of Natural Philosophy, Andrew Motte's translation revised by Florian Cajori (Berkeley and Los Angeles, 1934), 6. It might be said that, roughly, Locke's view of space and time was, and remained, the view of the "common people." Whether the common people were wrong was to be much debated in the ensuing centuries. It is of some significance that Locke's notes, which he made in September 1687 and March 1688, and which are preserved in the Bodleian Library (Mss. Locke c.33, fols. 19-20 and c.31 fols. 99-100) make no reference to Newton's commitment to absolute space and time. An account of the differing views of Locke and Newton on space and time, and their import, is something that I plan to give elsewhere. Dr. D. T. Whiteside has pointed out to me that the commitment to

LOCKE'S ESSAY AND NEWTON'S PRINCIPIA 223

Descartes that matter and space were the same thing. It was just one among very many positions which they held in common.15

III. Locke's Scientific Background. 6

We can say with confidence that the first edition of Locke's great work was not in any sense influenced by Newton. But what then of Laslett's statement that reading the Principia convinced Locke that he did not understand the natural world at all? (Quoted above, Section I). The fact is that Laslett offered us no evidence for this view. It is my belief that the evidence points in another direction. The fact is that Locke was acknowledged by his contemporaries to be an excellent and learned virtuoso. By the 1680's he had behind him a substantial record in sci- entific activity. It is not my intention to give a detailed account of Locke's many scientific qualifications, but some key points are these. Locke had been educated at Oxford just at the time when that university was very much concerned with the new science centered on the group around John Wilkins at Wadham College. Locke went up to Christ Church in 1652. In the years that he was there he was to become well acquainted with many of the very great scientists of the seventeenth century including Robert Boyle, John Wilkins, Thomas Willis, John Wallis, Robert Hooke, David Thomas, and Richard Lower. More important still, he was to become a collaborator with some of the most distinguished. From Locke's notebooks of the period we learn that even as an undergraduate he was beginning to take a keen interest in experimental physiology, probably through the influence of the physician Richard Lower.17 His interest in medicine developed rapidly; he attended the lectures of Thomas Willis and seriously considered taking up medicine professionally. Later

absolute space pervades the whole mathematical substratum of Book I of the

Principia. It is true that Locke's apparent failure to grasp this may well point to a failure on his part really to understand the Principia, at least at his first reading.

Locke's views on this see especially Essay II, XIII 12-16. Newton's views on matter were not clearly formulated in the first edition of the Principia. Rule III of the Regulae of the second edition has no corresponding hypothesis in the first edition, but Newton's rejection of the Cartesian position is manifest, and was of long standing. It is, for example, powerfully present in his paper De Gravitatione et

Aequipondio Fluidorum, probably written between 1664 and 1668. Cf. A. R. Hall and Marie Boas Hall, Unpublished Scientific Papers of Isaac Newton (Cambridge, 1962), 89-121.

16 There has in recent years been much important work done on the scientific

background to Locke's thought. Particularly relevant are: Maurice Cranston, John Locke. A Biography (London, 1957), Kenneth Dewhurst, John Locke (1632- 1704): Physician and Philosopher. A Medical Biography (London, 1963); the

many articles by Dewhurst on Locke's medical researches too numerous to list

here; the three articles by Axtell already cited. 17 Bodleian Library, MS Locke e4.

224 G. A. J. ROGERS

he was to collaborate with Lower when the latter was making some of his most important experiments,'8 and later still Locke was to collaborate with Thomas Sydenham.19 Locke, indeed, was a distinguished physician, but his interest in science was by no means confined to medicine.

Medicine required chemistry and this Locke set out to master.

Through his interest he soon became acquainted with Robert Boyle and by 1663 they were actively working together on scientific projects. Boyle's Memoirs for the Natural History of the Humane Blood (1683-4) is addressed to "the very Ingenious and Learned Doctor J. L."20

Later Newton and Locke were to be of mutual assistance in chemistry. When Newton showed interest in an experiment of Boyle's involved some "red earth" Locke sent him some, more, in fact, than Newton required. Newton wrote to Locke:

You have sent much more earth than I expected. For I desired only a speci- men, having no inclination to prosecute the process. For in good earnest I have no opinion of it. But since you have a mind to prosecute it I shall be glad to assist you all I can ....21

There is undoubtedly a question-mark over Locke's early mastery of mathematics, physics, and astronomy. Although Fox Bourne reports Locke as having attended lecture courses by both John Wallis and Seth Ward,22 we have no clear evidence of how much Locke really knew in these areas. Axtell, however, has gone a long way to establishing that Locke was capable of following much of the Principia when it was first published23 and has certainly supplied sufficient evidence for rejecting the traditional picture of Locke as a man totally ignorant of the mathe- matical sciences. It is often taken as conclusive evidence of Locke's lack of mathematical knowledge that he is said to have consulted Huygens as to whether the proofs in the Principia were mathematically sound.24 But in the light of Axtell's work this allegation must surely be treated with caution. It is well worth remembering that several other contemporaries of Newton admitted they could not follow all his mathematics, and some of those were mathematicians. David Gregory, later to be Professor of Mathematics in Edinburgh, wrote to Newton in September 1687 con- gratulating him on the Principia, but noting that "few would understand

18 Cf. Dewhurst, op. cit., 13-14. 19 Ibid., 34 ff. 20 On this see Dewhurst, "Locke's Contributions to Boyle's Researches on the

Air and on Human Blood," Notes and Records of the Royal Society, 17 (1962), 198-206.

21 Newton Correspondence. III, 215. The letter was written on 7 July, 1692. 22 Cf. H. R. Fox Bourne, The Life of John Locke, 2 vols. (London, 1876), I,

44ff., 55. 23 See esp. Axtell's "Locke, Newton, and the Two Cultures," 175ff. 24 The most usually cited source for this, almost certainly true, story is J. T.

Desaguliers, Experimental Philosophy (1763), I, viii.

LOCKE'S ESSAY AND NEWTON'S PRINCIPIA 225

it."25 Gilbert Clarke, another mathematician, wrote in the same month to Newton "I confess I do not as yet well understand so much as your first three sections."26 In December of the same year John Craig (d. 1731), yet another mathematician, wrote to a friend that he found understanding the Principia, "no small trouble."27 In the light of all this, Axtell is surely correct to emphasize the positive side of Locke's achieve- ment in coming to grips with the Principia, probably writing a clear and accurate, if necessarily superficial, review of it within a few months, and returning to it later to tackle more obstruse sections.

If the first edition of the Essay gives us no real sign of the positive impact of the Principia on Locke then in truth it cannot be maintained that subsequent editions are over-burdened with references to Newton's work or to positions which presuppose his discoveries. In the second edition of 1694, in the chapter Of Maxims of the fourth Book, Locke added a substantial section on the use of maxims which includes the

following:

They [i.e., maxims] are not of use to help men forwards in the advancement of sciences, or new discoveries of yet unknown truths. Mr. Newton, in his never enough to be admired book, has demonstrated several propositions, which are so many new truths, before unknown to the world, and are further advances in mathematical knowledge; but, for the discovery of these, it was not the general maxims, What is, is; or, The whole is bigger than a part, or the like that helped him. These were not the clues that led him into the dis- covery of the truth and certainty of those propositions. Nor was it by them that he got the knowledge of those demonstrations, but by finding out inter- mediate ideas that showed the agreement or disagreement of the ideas, as expressed in the proposition he demonstrated....28

Here Locke uses the mathematics of the Principia to support a general point he wishes to make, and indeed which he had made in the first edition, against all those who wish to claim that knowledge is dependent on having knowledge of general maxims-a thesis that Locke was bound to reject as he grounded all knowledge in experience of the particular.

We have to wait until the fourth edition of the Essay, in 1700, before we find another clear example of the impact of the Principia on Locke's

Essay. In Book II, Chapter VIII, Section 11, Locke in the earlier editions had written:

The next thing to be considered, is, how Bodies operate one upon another,

25 Newton, Correspondence, II, 484. 26 Ibid., 485. 27 Ibid., 501. I. Bernard Cohen in his Introduction to Newton's 'Principia'

(Cambridge, 1971) suggests that Newton may have had Locke specifically in mind when he wrote an emendation which he contemplated making to the introductory paragraph of Book III of the Principia. It is possible that Cohen is right but there were so many eminent men who could not follow all of Newton's proofs that the

suggestion seems unlikely. Cf. op. cit., 147-48. 28 Essay, IV, VIII, 11. Yolton edition, II, 199-200.

226 G. A. J. ROGERS

and that is manifestly by impulse, and nothing else. It being impossible to conceive, that Body should operate on what it does not touch, (which is all one as to imagine it can operate where it is not) or when it does touch, operate any other way than by Motion.

In the fourth edition this was changed to:

The next thing to be considered is, how bodies produce ideas in us; and that is manifestly by impulse, the only way which we can conceive bodies operate in.

The generalization about the ability of bodies to operate without contact has disappeared.

The explanation for this change is to be found in Locke's third letter to Bishop Stillingfleet. It reveals a way in which Newton's book played a part in modifying Locke's ideas. But it does not reveal a funda- mental reappraisal. Rather it shows that Newton's book added further confirmation of a general position to which Locke already subscribed. The general position was that one cannot determine a priori what the

powers of objects are except where there is a contradiction implied. Locke wrote:

.. You ask, how can my idea of liberty agree with "the idea that bodies can operate only by motion and impulses?" Answ. By the omnipotency of God, who can make all things agree, that involve not a contradiction. It is true I say, "that bodies operate by impulse and nothing else." And so I thought when I writ it, and can yet conceive no other way of their operation. But I am since convincd by the judicious Mr. Newton's incomparable book, that it is too bold a presumption to limit God's power, in this point by my narrow conceptions. The gravitation of matter towards matter, by ways in- conceivable to me, is not only a demonstration that God can, if he pleases, put into bodies, powers and ways of operation above what can be derived from our idea of body, or can be explained by what we know of matter, but also an unquestionable and everywhere visible instance, that he has done so. And therefore in the next edition of my book, I shall take care to have that passage rectified.29

The third letter was published in 1699, the year before Locke's alterations appeared in the Essay.

The examples show that the Essay was not seriously altered by Locke as a result of his reading and comprehension of the Principia. It is a

point of some weight for a full appreciation of the Essay's significance. In so far as the approaches to science and knowledge revealed in the Essay and the Principia are the same, certainly with respect to all the editions of the Essay and the first edition of the Principia, then this is because their authors shared a common outlook rather than because one was greatly influential on the other. To suggest, as some have done, that

29 The Works of John Locke, 7th ed. (London, 1768), I, 754.

LOCKE'S ESSAY AND NEWTON'S PRINCIPIA 227

the Principia was immediately influential because we can recognize its impact on the Essay is totally to misunderstand the background of both works and it leads to a wrong appraisal of the place which the Essay occupies in seventeenth-century thought.30

Let us now return to Laslett's suggestion that Locke was convinced

by his reading of the Principia that he really did not understand the natural world at all. We may surely grant that an inability to follow all of the mathematics of the Principia is not in itself reason to suppose that Locke would feel that he did not understand the natural world. We must of course recognize that there are degrees of comprehension, and that there are two different things to be understood, the world itself, and Newton's account of it. It is, I believe, certain that Locke felt he under- stood the natural world a good deal better after reading the Principia, even though, as no doubt he would have gladly conceded, he had neither tried nor been able to follow all of Newton's mathematics. Here the wording of Desaguliers' account of Locke's consultations with Huygens is relevant. The passage reads:

The celebrated Locke, who was incapable of understanding the 'Principia' from his want of geometrical knowledge, inquired of Huygens if all the mathe- matical propositions in that work were true. When he was assured that he might depend upon their certainty, he took them for granted, and carefully examined the reasonings and corollaries deduced from them. In this manner he acquired a knowledge of the physical truths in the 'Principia', and became a firm believer in the discoveries which it contained. In the same manner he studied the treatise on 'Optics', and made himself master of every part of it which was not mathematical.31

It is almost certain that this is the source for the view that Locke was a keen student of the Opticks, even though, as we have already seen, it did not appear until shortly before his death. But that apart, one very inter-

30 Despite my admiration for his important contributions to a correct under-

standing of the relation between Locke and Newton I cannot therefore agree with Axtell's judgement that in the Essay "there is considerable evidence-both internal and external-that Locke was deeply influenced by Newton's achievements, but

especially by the whole methodology that lay behind the Newtonian synthesis." ("Locke's Review of the Principia," 159-60.) It is sometimes suggested that the

really important effect of the Principia on Locke was that it made him aware of the power of mathematical deduction, and therefore of deduction generally. I can ifind no support for this in the Essay, and evidence to the contrary. Those passages in the Essay where Locke speaks of the power of deductive knowledge are often

clearly anticipated in drafts of the Essay written in 1671. Thus in Essay IV, II, 9-

14, Locke says that "demonstration" (i.e., deductive reasoning as exhibited in

geometry) can be carried into other areas. This argument is anticipated in Draft

B, ? 45 and 46. 31 As well as in the Desaguliers reference, already cited in Note 24, the story

is reported in Sir David Brewster's Memoirs of the Life, Writings, and Discoveries

of Sir Isaac Newton, 2 vols. (Edinburgh and London, 1815), I, 339.

228 G. A. J. ROGERS

esting facet of the story is that Locke is reported as consulting Huygens about only the mathematics of the Principia and not about any other aspect of the work. As is well known, Huygens was not wholeheartedly a supporter of Newton.32 His attitude, along with other Cartesians, anticipated that of Leibniz in several particulars. But Locke was clearly not prepared to accept Huygen's verdict on the work. Rather, he sat down to study it, and, the mathematics granted, to assess it for himself.33

What exactly was Locke's reaction to the Principia when he first read it? We have several clues, but none of them suggest any kind of major reappraisal on Locke's part. We have already seen that the draft of the Essay received no important changes. But we also have what is almost certainly Locke's review, written in 1688. The review begins by indicat- ing that Newton's book is part of a recent, but already established, approach, namely the geometricizing of mechanics. The Principia, Locke was saying, was not new in terms of its method, but it was new in terms of the depth to which that method had been taken, and although there are some innovations of method in the Principia, Locke's general point is surely sound. But it is worth emphasizing that the development of such a geometrical method was, as we have already seen, an aspiration which Locke held prior to his reading the Principia. (See Note 30 above.) In his review by quoting the Scholium to Principia Book I, Proposition LXIX, Locke also makes a point of the fact that Newton did not mean by attraction anything other than:

l'effort que font les corps, pour s'approcher l'un de l'autre, soit que cet procede, ou de l'action des corps qui tendent l'un vers l'autre, ou qui se choquent reciproquement par les corpuscules qu'ils exhalent; soit qu'il se fasse par Faction de l'Ether, par celle de l'air, ou de quelque autre milieu sensible, ou insensible, dans lequel ces corps nagent, & qui les pousse Fun contre l'autre. Je me sers, dans le meme sens general, du terme d'impulsion.34

32 Huygens' attitude towards the Principia was judicial in his Discours sur la cause de la Pesanteur (1690) but he was less polite in a letter to Leibniz. Cf. Oeuvres completes de Christiaan Huygens publiees par le Societe hollandaise des Sciences (The Hague, 1888-1950, 22 vols.), IX, 538.

33 When Locke first read the Principia in 1687, he was in Rotterdam. Huygens was also then in Holland, and it is probable that they met there. It is possible that

they first met much earlier, in 1677, when they were both in Paris. It may be

objected that what is not possible is to understand the Principia without understand-

ing the mathematics, for the simple and sufficient reason that it is a work of mathematics and nothing else. It must, however, be remembered that Desaguliers was himself attempting to show that it was possible to understand Newton's philos- ophy without understanding mathematics, and he tells the story about Locke precisely to illustrate that possibility.

34Bibliotheque Universelle & Historique de l'Annee 1688, 439. The review which covers pages 436-450 is over 2000 words in length. For contrasting assess- ments of it see Axtell, "Locke's Review of the 'Principia'," cited in Note 6, and Cohen, An Introduction to Newton's 'Principia', cited in Note 27, 145-47. Although

LOCKE'S ESSAY AND NEWTON'S PRINCIPIA 229

This underlines the fact that Locke was well aware that Newton was basing his argument on what he took to be well established empirical concepts, once again entirely in keeping with the empiricist approach of Locke himself.

The suggestion is, therefore, that what Locke found in the Principia was the exemplification of a method to which he himself already sub- scribed. He already believed that a combination of observation, general- ization or induction, and deduction was the only route to knowledge of nature and that the Principia exhibited just that method in its most fruitful manner.35 It was thus perfectly natural for him to turn to it as an example when he wished to stress that, contrary to the Ramist tradi- tion, but entirely in keeping with that of Bacon, there was a great differ- ence between "the method of acquiring knowledge and of communicating, between the method of raising any science and that of teaching it to others as far as it is advanced."36 It was not on maxims that Newton's science rested, said Locke, but on showing by a chain of related ideas how one idea was necessarily connected to another.

Mr. Newton, in his never enough to be admired book, has demonstrated several propositions, which are so many new truths before unknown to the world, and are further advances in mathematical knowledge; but, for the discovery of these, it was not the general maxims, What is, is or The whole is bigger than a part, or the like that helped him.... but by finding out inter- mediate ideas that showed the agreement or disagreement of the ideas as expressed in the propositions he demonstrated.37

these assessments have rather different objectives I would tend to support Axtell's rather than Cohen's. Cohen rather underplays the function of the review in the Bibliotheque Universelle. It must be remembered that Locke was in a sense trying to sell the Principia to a Cartesian-orientated public, who were, nevertheless, unlikely in general to be mathematically sophisticated. It is worth emphasizing that the non-mathematician, Locke, grasps immediately a crucial aspect of Newton's

presentation which, notoriously, the mathematician Roger Cotes, in his Preface to the second edition of the Principia, completely missed, much to the annoyance of Newton. It is possible to doubt that Locke was the author of the review for there is no conclusive final evidence that he did write it. However, as Axtell argues, the comparison between Locke's manuscript notes and the published review, the

presence of Locke in Holland, the known fact that he did write reviews for the

journal, and the lack of any other candidate makes quite a strong case. 35 It is worth underlining the fact that mathematics was for Locke not a

discipline which had a unique method. It was exactly on a par with any other deductive argument which moved from idea to idea via necessary connection. It was precisely because of this that Locke believed that it was in theory possible to have deductive systems of physics in areas which were not mathematical. Once this is taken, then the otherwise puzzling remarks in Essay, IV, II, 9 ff. become clear.

36 Essay, IV, VII, 11. On the Ramist tradition and on Bacon see, for example, Lisa Jardine, Francis Bacon: Discovery and the Art of Discourse (Cambridge, 1974) esp. chapters 1, 2, and 3.

37 Essay, IV, VII, 11.

230 G. A. J. ROGERS

It would thus appear that to read the Principia was not for Locke any sort of traumatic experience. Quite the contrary. It confirmed for him all his own methodological conclusions. The only way in which natural

philosophy could be advanced was by the methods of observation and deduction, and, although there were definite limits to what could be learnt by the application of such techniques, Newton had shown that they were, nevertheless, capable of producing the most wonderful results. The Principia was for Locke the vindication of a general methodological approach to which he had subscribed for perhaps twenty years.

IV. Locke and Newton: their personal acquaintance. There is no evidence to suggest that Locke met Newton prior to the

former's return from Holland in 1689 after his absence since 1683. It is, however, just possible that they did meet before Locke's departure. Locke was elected Fellow of the Royal Society in 1668 and remained in London until November 1675, except for a month which he spent in France. Newton was elected a Fellow in January 1671/2, but he had been in London in 1669 and in February 1675. Whether on either of these occasions they did actually meet can only be a matter of conjecture. I have been able to uncover only one piece of documentary evidence which connects them prior to Locke's stay in Holland. In one of Locke's

commonplace books for the years 1676-94 there occurs the following entry: "Aqua the weight of water to air is as 950 to one. Mr. Newton."38 The entry is dated 1680. But it is unlikely that this information was conveyed personally to Locke from Newton. As it appears to have no

published source, it is probable, that it was conveyed to Locke via a third party, and the most likely third party is Robert Boyle with whom Newton was then in correspondence, and with whom Locke was then collaborating.39 By this stage Locke would already be familiar with Newton's work in optics which had been published in the Royal Society Transactions in 1672.

Whatever the truth about their earlier contact, Locke and Newton did not become friends until much later, for it was not until after Locke's return from Holland at the beginning of 1689 that they became well

38 Bodleian Library, MS Locke C.42A f.244. 39 Although Boyle is the most probable source he is not the only possible one.

Isaac Barrow was another. Locke met Barrow in 1672 and Barrow gave Locke a

copy of his Lectiones Geometricae (1670). The book is inscribed "Ex Dono Authoris Viri cujus eruditiones pars minima est mathesis laudis doctrina." On this see John Harrison and Peter Laslett, The Library of John Locke, 2nd ed. (Oxford, 1971), 44-73. It is totally unlikely that Barrow would have conveyed this informa- tion from Newton to Locke, but Barrow's acquaintance with Locke at this stage establishes a contact between Locke and Trinity College. For Barrow's influence on Newton's views on space and matter see E. W. Strong, "Barrow and Newton," Journal of the History of Philosophy, 8(1970), 155-72.

LOCKE'S ESSAY AND NEWTON'S PRINCIPIA 231

acquainted. It is traditionally assumed that Locke and Newton met in late 1689 or early 1690 at the salon of the Earl of Pembroke. Although there is no positive evidence for this it seems entirely plausible. Wherever it was, Locke and Newton had soon established a personal contact which was to become a friendship lasting until Locke's death. They must soon have recognized that they had much in common. Both were keenly interested in the natural sciences, though Locke's interests were wider and shallower than Newton's, both were deeply religious and believed that religion was capable of rational comprehension. Their family back- grounds were far from dissimilar. Both came from remote rural areas and both were from modest middle-class homes. Both remained life-long bachelors, both were disinclined to rush into print. More specifically, their intellectual outlooks were remarkably alike: both were Whig in politics; both were opposed to enthusiasm in the matter of religion; both, whilst strongly attracted to the philosophy of Descartes, were in fact set against what they took to be the fundamental flaws both in Cartesian theory and in Cartesian methodology; both were committed to the method in science which found expression in the work of the Royal Society.40

40 Fully to document the claims made here in respect of the shared hostility to Cartesian methodology and the shared support of the method in science which found expression in the Royal Society would itself require a long paper. There are, however, some brief pertinent remarks which may be made. Both Locke and Newton rejected the Cartesian view that a theory in science can be accepted as established if it can be shown that the theory is compatible with all known empirical data. Descartes claimed in the Principles of Philosophy (Part IV Principle CCIV) that "I believe that I have done all that is required of me if the causes I have

assigned are such that they correspond to all the phenomena manifested by nature." It was precisely this type of hypothetical explanation, which found

expression in the work of many Cartesians, such as Rohault and Huygens, to which Newton was so strongly opposed. Newton's rejection of this "hypothetical" method not only found expression in the Regulae, the General Scholium of the Principia, and the 31st Query of the Opticks, but also in his manuscripts. The following two

passages are, I believe, representative examples, both taken from drafts for the later Queries: 1. "Could all the phenomena of nature be (evidently) deduced from

only three or four general suppositions there might be great reason to allow those

suppositions to be true: but if for explaining every new Phenomenon you make a new Hypothesis if you suppose yt ye particles of Air are of such a figure size and frame, those of water of such another, those of vitriol of such another, those of Quicksilver of such another, those of flame of such another, those of Magnetick effluvia of such another. If you suppose that light consists in such a motion pres- sion or force and that its various colours, are made by such & such variations of the motion & so of other things: your Philosophy will be nothing else than a

systeme of Hypotheses. And what certainty can there be in a Philosophy wch consists in as many Hypotheses as there are Phaenomena to be explained. To explain all nature is too difficult a task for any one man or even for any one age. Tis much better to do a little with certainty & leave the rest for others that come after, than to explain all things by conjecture without making sure of anything: And there is no other way of doing any thing with certainty than by drawing con-

232 G. A. J. ROGERS

It is not too much of an exaggeration to say that a detailed account of the shared intellectual attitudes of Locke and Newton would go a long way to describing most of the major intellectual forces which shaped the eighteenth century.

University of Keele.

clusions from experiments & phaenomena untill you come at general Principles & then from those Principles giving an account of Nature. Whatever is certain in Philosophy is owing to this method & nothing can be done without it." (U.L.C. Add MS. 3970 f.479.) 2. ". .. if without deriving the properties of things from Phaenomena you feign Hypotheses & think by them to explain all nature you may make a plausible systeme of Philosophy for getting your self a name, but your systeme will be little better than a Romance." (U.L.C. Add MS. 3970 f.480.)

These quotations do not, of course, establish that Newton did in fact practice the method he preached. There is mounting evidence that often he did not. See, for example, R. S. Westfall, "Newton and the Fudge Factor," Science, 179 (1973); D. T. Whiteside, "Newton's Lunar Theory: From High Hope to Disenchantment," Vistas in Astronomy, 19 317-28. But I believe that at least we can say that Newton's

"logic of justification," in contrast with his "logic of discovery," was entirely at one with principles argued by Locke and widely accepted amongst the early members of the Royal Society.

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