is a state of insusceptibility to change for the worse and to destruction by another thing or by the thing itself qua other, i.e. by a principle of change. In all these definitions is implied the formula of potency in the primary sense. — And again these so-called potencies are potencies either of acting merely or of being acted on, or of acting or being acted on well, so that even in the formulae of the latter the formulae of the prior kinds of potency are somehow implied.
Obviously, then, in a sense the potency of acting and of being acted on is one (for a thing may be 'capable' either because it can be acted on or because something else can be acted on by it), but in a sense the potencies are different. For the one is in the thing acted on; it is because it contains a certain motive principle, and because even the matter is a motive principle, that the thing acted on is acted on, one thing by one, another by another; for that which is oily is inflammable, and that which yields in a particular way can be crushed;[1] and similarly in all other cases. But the other potency is in the agent, e.g. heat and the art of building are present, one in that which can produce heat and the other in the man who can build. And so in so far as a thing is an organic unity, it cannot be acted on by itself; for it is one and not two different things. And want of potency, or powerlessness, is the privation which is contrary to potency of this sort, so that every potency belongs to the same subject and refers to the same process as a corresponding want of potency. Privation has several senses; for it means (1) that which has not a certain quality and (2) that which might naturally have it but has not it, either (a) in general or (b) when it might naturally have it, and either (i) in some particular way, e.g. when it completely fails to have it, or (ii) when it in any degree fails to have it. And in certain cases if things which naturally have a quality lose it by violence, we say they suffer privation.
- ↑ i.e. the event would not happen if the passive factor were different. What is oily cannot necessarily be crushed, nor what is yielding burnt.
