 Without trying to proceed further with this issue here, we can see that whichever of these views is ultimately adopted, it remains the case that Leibniz’s theory of perception involves something very distinctive in an age dominated by Descartes’ theory of ideas, the thesis that there are some perceptions of which we are not conscious, the much-discussed petites perceptions. Although Leibniz may not have been the first to propose such an idea (Aquinas, for example, might have had a similar view; see his Summa Theologiae, I-II, q.1, art.3), and although the view in his hands did not have the explosive quality that it did in the hands of Freud, the thesis remains an intriguing and important part of his philosophy of mind. Indeed, the Preface of the New Essays concerning Human Understanding contains as strong a statement as one is likely to find about the centrality of this view in a particular metaphysical system. Among other things, Leibniz makes it very clear that it is not just lower simple substances that have such unconscious perceptions but also human minds.