The history of the Nouveaux essais
Within five years of the first appearance of Locke's Essay Concerning Human Understanding (1690), Leibniz had read at least some of it, and had written several pages of comments – some appreciative, some mildly critical – upon parts of the work, allowing an intermediary to pass them on to Locke. The latter received them sourly, writing to a friend with a sceptical allusion to Leibniz's ‘great name’, and concluding that ‘even great parts will not master any subject without great thinking, and even the largest minds have but narrow swallows’ (Locke to Molyneux, April 1697). The letter containing that remark was published in 1708, and Leibniz later wrote: ‘I am not surprised by it: we differed rather too much in principles’ (Leibniz to Rémond, March 1714).
Leibniz's interest in Locke's work is abundantly shown by his correspondence in the 1690s, by his re-working the comments mentioned above, and by his writing a fresh set of remarks on Books 1 and 11 of the Essay, as well as (in 1698) a longer commentary on the controversy which the Essay had stirred up between Locke and Stillingfleet, the Bishop of Worcester.
The English language must have been something of a barrier between Leibniz and Locke's long, difficult book. In a letter admitting the imperfections in his French, he wrote: ‘I only wish I had the same knowledge of the English language; but not having had the occasion for it, the most I can manage is a tolerable understanding of books written in that language’; and on p. 462 of the present work there is a small but striking indication of his not being at home with English.