The relationship between John Locke and Isaac Newton, his co-founder of, in the apt phrase of one recent writer, ‘the Moderate Enlightenment’ of the eighteenth century, has many dimensions. There is their friendship, which began only after each had written his major work, and which had its stormy interlude. There is the difficult question of their mutual impact. In what ways did each draw intellectually on the other? That there was some debt of each to the other is almost certain, (...) but its exact extent is problematic. Questions may be asked over a whole range of intellectual issues, but not always answered. Thus their theology, which was in many respects close, and which forms the bulk of their surviving correspondence, may yet reveal mutual influence. There is the question of their political views, where both were firmly Whig. But it is upon their philosophy, and certain aspects of their philosophy in particular, that this paper will concentrate. My main theme is the nature of their empiricism, and my main contention is that between them they produced a powerful and comprehensive philosophy. (shrink)