  For Leibniz, the simplicity and unity of the mind still allows for the multiplicity of perceptions and appetitions. The multiplicity, however, should not only be interpreted as diachronous but also synchronous; that is, the mind despite its simplicity and unity has within it at any time an infinity of different petites perceptions. A human being, in a waking state, is conscious of particular perceptions, but never all. And here we see that Leibniz's doctrine is important, insofar as it offers a contrast to the Cartesian theory of the mind. According to Leibniz, the mind is always active, for there are always perceptions present to it, even if those perceptions are minute and do not rise to such a level that we are cognizant of them. Thus, even in a deep and dreamless sleep, the mind is active, and perceptions are in the mind. Moreover, if Descartes really did advocate the perfect transparency of the mind, then it should be clear that Leibniz allows for a subtler picture of mental contents: there are many things in the mind that are confused and minute and to which we do not always have complete access.