Isaac Newton and John Locke: in public and in private

by Mark Goldie

During the eighteenth century the names of Isaac Newton and John Locke were often linked as shining beacons of the Enlightenment, the latter revolutionising philosophy as surely as Newton had transformed physics. In his preface to An Essay Concerning Human Understanding (1689) Locke described his own role modestly as that of an ‘under-labourer in clearing the ground a little, and removing some of the rubbish’ that lies in the path towards knowledge, making way for such ‘master-builders’ as ‘the incomparable Mr Newton’. It was a proclamation that did much to promote science to ascendancy as the paradigm of modern knowledge

Locke (1632-1704) was a prodigious intellectual who contributed not only to philosophy, but also to political theory, economics, education, and theology. In his annus mirabilis of 1689 he published, as well as the Essay, his two other best-known works, the Two Treatises of Government and A Letter Concerning Toleration. It was the year of the Glorious Revolution, which enabled Locke to return from exile in The Netherlands, where he had fled in 1683 in fear for his life, because of his involvement in the Whig movement. Newton, meanwhile, had withstood the regime of the House of Stuart at home, by his defence of the autonomy of the University of Cambridge. After the Revolution both men were in favour with the new regime and were drawn into the arena of national policy-making. Their lives soon intertwined, bound together not only by demands for their expertise, but also by their mutual striving to protect their time for scholarship and philosophical speculation.

The two men were fast friends, despite their touchiness. Their relationship survived an imbroglio in 1693, when, bizarrely, Newton accused Locke of seeking to ‘embroil me with women’, and, more seriously, of undermining the foundations of morality in the Essay, such that ‘I took you for a Hobbist’ – in other words, he took Locke to be a moral relativist of the kind the notorious Thomas Hobbes was reputed to be. Newton was going through a bad patch, though he was not alone in being suspicious of Locke’s ethics. Locke forgave him, and in 1703 remarked, ‘I have several reasons to think him truly my friend, but he is a nice man to deal with, and a little too apt to raise in himself suspicions where there is no ground’. It was an astute judgement - ‘nice’ here means tricky or particular.

They appear to have met under the aegis of Charles Mordaunt, earl of Monmouth and later earl of Peterborough, a leading, though mercurial, figure in post-Revolution Whig politics. As well as being a patron of intellectuals, he was a keen ‘projector’, a jargon word of the 1690s: he was ready to entertain schemes, not always sound, for the public good. Newton was making his first bid for appointment to a lucrative public office, and Locke was willing to recommend him to Monmouth. Newton was a tyro in these matters, and Locke’s factotum Robert Pawling said that Newton was like a blushing youth awkwardly broaching his affection for a lady. Pawling reports having to push Newton through a door into the earl’s presence. But Newton soon learnt the proper courtesies. Lord and Lady Monmouth’s ‘favour is such that I can never sufficiently acknowledge it’. Already, in 1691, Newton had in mind a post at the Mint: the office of Comptroller was mentioned, though there was no vacancy at the time. (He was not interested, when it was suggested, in the headmastership of London’s Charterhouse school.) In 1695, Locke himself appears to have sought the Comptrollership, but was told that Newton was in line for it. In fact, it was to the Wardenship that Newton was appointed in the following year. Locke never held office at the Mint, but it was plausible that he should have aspired to it, because, by then, he was also an expert on the currency.

The two men’s earliest intellectual interactions did not, however, concern money, or physics, or philosophy, but theology. In 1690 Newton sent Locke his essay concerning textual corruptions in the New Testament in passages that were used by the orthodox to defend the Trinity: the doctrine that the Godhead is comprised of three persons, the Father, Son, and Holy Ghost. Locke passed the essay to his friend, the publicist Jean Le Clerc, at Amsterdam, for publication, although Newton soon forbad printing, and it did not appear until 1754. The essay provides evidence that both men may have been ‘Socinians’ – doubters of the divinity of Christ. Next Newton sent Locke, for comment, his interpretation of apocalyptic passages in the Old Testament book of Daniel and the last book of the New, Revelation. Later, Newton returned the favour by commenting on Locke’s draft of commentaries on St Paul’s Epistles. Modern scholarship on Newton has been emphatic that we must take seriously his deep theological preoccupations. Locke wrote: ‘Mr Newton is really a very valuable man not only for his wonderful skill in mathematics but in divinity too and his great knowledge in the scriptures wherein I know few his equals’.

But it was the currency crisis which, in 1695, brought both men into the heart of national policy-making. When Damaris Masham wrote her memoir of her intimate friend Locke she singled out as his greatest contributions to the ‘public good’, not his Two Treatises, but the tracts he had written about ‘toleration and recoinage’ - religious conciliation and sound currency. Indeed, when a pamphleteer, in 1696, praised Locke’s ‘excellent political maxims’, he had in mind, not the Two Treatises, but the tracts on money, taxation, and economics.

By the mid-1690s the currency was in a parlous state, and the monetary crisis threatened to destroy the government’s ability to sustain its large-scale war against France. Most coinage for commercial transactions was made of silver. Before modern times the dependability of coinage relied on its precious metal content, silver or gold; coins were not made merely of cheap alloy having only a nominal value. The monarch’s stamp on a coin was supposed to guarantee real and not just ‘denominative’ value. But by the 1690s the market value of silver was higher than the face value of silver coins. This encouraged clippers to pare the edges of coins in order to retrieve the precious metal, or even the wholesale melting down of coins. The temptations of quick gain overwhelmed even the most punitive of legislation against clippers and ‘coiners’. The problem was only partially combatted by the recently invented device of issuing coins with milled edges; older coins were still legal tender. People were reluctant to accept clipped coins, and coin in general was in short supply for everyday trade, since clandestine melting outstripped the Mint supply.

Locke and Newton were among several experts who were invited to advise the government on the recoinage and their reports are today among the Goldsmiths Library manuscripts. The advisers included Sir Christopher Wren and several of London’s influential merchants. The Treasury secretary William Lowndes recommended devaluation, setting the denominative value above the market value. But Locke’s intervention was decisive in persuading the government to recoin at the existing standard.[1] The initial impact was dire. The Mint was slow to produce new coinage. The public were at risk of personal loss in surrendering old coinage to the authorities. Rents and debts went unpaid. It took several years before equilibrium was restored. Miraculously, despite wartime pressures, the outflow of cash to pay England’s continental army and allies, and the immense cost of recoinage, government finances did not collapse. Monetary theorists have argued the wisdom or folly of Locke’s and his rivals’ positions ever since.

Practically all the experts held that a recoinage was necessary, though some, including Newton, thought that withdrawal of the old coinage should be staggered over time. He differed from Locke on the crucial question of devaluation. He argued that raising the denominational, or ‘extrinsic’, value of the coin would make clipping and melting less profitable; it would allow for a greater quantity of coin available for trade; and it would be cheaper to undertake. His detailed proposals for ‘quick dispatch at the Mint’ look like a job application.

Despite these differences, the two men continued to collaborate on currency matters, Newton as Warden, and Locke, from 1696, a member of the Board of Trade and Plantations. In 1698 Locke signed a Board memorandum, advised by Newton, concerning adjusting the price of gold guineas.

Locke and Newton coincided in the public domain in other spheres too. They were drawn into the controversy over the colonial relationship of England and Ireland, as is apparent from a memorandum of Newton’s discovered in recent years. In 1698 the Irish ‘Patriot’ William Molyneux published The Case of Ireland, asserting Ireland’s autonomy, under the crown, and right to legislate for itself. Molyneux cited Locke’s Two Treatises, shrewdly turning its Whig principles against the power of the imperial overlord. When did Ireland ‘consent’ to be ruled by England? Locke himself remained silent on the applicability of his book to colonies, though he clearly thought Molyneux’s intervention foolish. But Locke’s Whig associates publicly and vehemently attacked Molyneux. Their position amounted to saying that revolution for regime change was fine for England, but not for England’s possessions. Newton’s ‘The Case of the Parliament of Ireland’ is among his Mint papers and argues bluntly that Ireland is ‘subordinate’ to England. Like most centralising English ‘statists’, Newton refused the possibility of plural national parliaments, each equal under the crown, insisting instead – and it is a non sequitur – that because Ireland is under the crown ‘by consequence’ it is subject to legislation by the English Parliament. Newton partly had in mind the interest of the Mint in having complete control over the currency.

Locke’s final act at the Board of Trade, called back a few weeks after his formal resignation in 1700, was to advise on the possibility of establishing a Mint in North America. Neither man recommended it.

The evidence for Locke’s and Newton’s long association is extensive. Locke sent Newton complimentary copies of his new publications. Newton visited Locke at Oates more than once, and Locke’s only known visit to Cambridge was to see Newton. A few days before Locke’s death, his close friend, heir and executor, Peter King, reported to him that he had been with Mr Newton to discuss the design of medals to celebrate England’s victories over the French – the Battle of Blenheim and the seizure of Gibraltar.