The word form has had various usages in philosophy. It has been used to translate the Platonic idea (eidos), the permanent reality which makes a thing what it is, in contrast with the thing’s particulars, which are finite and subject to change. Whether Plato understood these forms as actually existent apart from all the particular examples, or as being of the nature of immutable physical laws, is a matter of controversy. For practical purposes, Aristotle was the first to distinguish between matter (hyle) and form (morphe). To Aristotle matter is the undifferentiated primal element: it is rather that from which things develop than a thing in itself. The development of particular things from this germinal matter consists in differentiation, the acquiring of particular forms of which the knowable universe consists (cf. causation for the Aristotelian formal cause). The perfection of the form of a thing is its entelechy in virtue of which it attains its fullest realization of function (De…