In other words, each individual substance has a complete individual concept (CIC), which contains (or from which are deducible) all predicates true of it past, present, and future. Leibniz asks his reader to consider the case of Alexander the Great. On his view, God can, as it were, look at the complete individual concept of Alexander and see that he conquered Darius and Porus, that he was the student of Aristotle, that his armies would march into India, and so on. For our purposes, it will suffice to think of the CIC as the essence of an individual substance and to think of God as able to survey all essences of all individual substances. (The issue is, in fact, vexed; for insightful presentations of views rivaling that presented here, see Sleigh 1990 or Cover and Hawthorne 1999.)  Further, according to Leibniz, one of the consequences of this view of the nature of an individual substance is that no two substances can be qualitatively identical and differ numerically.  In other words, the Principle of the Identity of Indiscernibles (PII) follows from this conception of the nature of substance, and PII entails that, for any possible world, there is at most one instance of a CIC.