For instance...

For instance, an embryo possessing the potential to become a human being is closer to humanity than a lump of food, which assesses the potential for changing into an embryo, and the potential possessed by the former is greater than what is possessed by food. It is obvious that this potential, which is something existing in external reality, is not something substantial (jawhar) subsisting bv itself. Rather, it is an accident that subsists through something else.

We will call it ‘potentiality’ (quwwah) and its substratum, ‘matter’ (mâddah). Thus everything that comes into existence in time consists of ‘matter’ that precedes it and carries the potentiality of its existence. It is necessary that ‘matter’ should not be unreceptive to the actuality whose potential it bears. Hence it is in itself the potentiality for receiving the actuality whose potential it bears.

For if matter were to have an actuality of its own, it would refuse to accept any other actuality. Thus it is a substance (jawhar) whose intrinsic actuality is the potentiality for things. However, in order to be a substance endowed with potentiality, it subsists through another actuality. When the actuality for which it has the potentiality comes into being, the earlier actuality disappears, giving its place to the new actuality. An example of it is water.

When it changes into vapour, its aqueous form - which earlier sustained the matter that now bears the form of vapour - disappears and is replaced by the gaseous form through which the matter that earlier bore the potential to become vapour is now sustained. The matter of the new emergent actuality and that of the earlier defunct actuality is one, for otherwise we would have to regard it as coming into being with the emergent actuality.

This would necessitate another potential and another matter, and this entails an indefinite regress. Thus a single emergent thing would require an infinite number of potentials and matters, and this is inadmissible. A similar difficulty arises if we consider matter as having come into existence in time (hadits zamânî). From the above discussion it becomes clear that, first, everything that comes into existence in time has a ‘matter’ that bears the potentiality for its existence.

Second, the matter of things that come into existence in time is one and common to them.