DESCARTES TO BERKELEY What assures me that the Cogito is correct? Only that I see clearly that it is true Whenever I conceive something clearly and distinctly, I am assured of its truth But when we turn to material objects, we Wnd that of all their properties the only ones we clearly and distinctly perceive are shape, size, and movement So Descartes gains his second main thesis, that matter is extension in motion But what guarantees the principle that whatever I see clearly and distinctly is true? Only the truthful nature of the God to whom I owe my existence as a thinking thing So establishing the existence of God is a necessary part of Descartes’ system He oVers two proofs that there is a God First, I have in myself the idea of a perfect being, and this idea cannot be caused in me by anything less than a being that is itself perfect Second, to be perfect a being must include in itself all perfections; but existence is a perfection, and therefore a perfect being must exist.1 Like Bacon, Descartes compared knowledge to a tree, but for him the tree’s roots were metaphysics, its trunk was physics, and its fruitful branches were the moral and useful sciences His own writings, after the Discourse, followed the order thus suggested In 1641 he wrote his metaphysical Meditations, in 1644 his Principles of Philosophy, which is a pruned version of the physical system of The World, and in 1649 a Treatise on the Passions, which is largely an ethical treatise The Meditations contain a full statement of the system sketched in the Discourse Before publication the text was sent to Mersenne to circulate for comment to a number of scholars and thinkers Six sets of objections were received They were printed, with replies from Descartes, in a long appendix to the Wrst edition of 1641, which thus became the Wrst peer-reviewed work in history The objectors were a varied and distinguished group: apart from Mersenne himself they included a scholastic neighbour in Holland, an Augustinian theologian from Paris, Antoine Arnauld, plus the atomist philosopher Pierre Gassendi, and the English materialist and nominalist, Thomas Hobbes Criticisms of the Meditations continued to come in after publication, and critical reaction was not only literary The rector of Utrecht University, Gisbert Voetius, denounced Descartes to the magistrates as a dangerous Descartes’ natural theology is considered in detail in Ch 10 37