change in the subject that is affected by the change. The converse of this is the potentiality for being unaffected or active potentiality. This is the principle of change in the subject that initiates the change. An example of a passive potentiality would be the combustibility of a match and an example of an active potentiality would be the brightness of a light bulb. Both passive and active potentialities are the same in that they are primary, but they clearly differ because, as primary potentialities they hold different relationships (active and passive) to the other thing. Aristotle argues that a thing can contain both a passive and an active potentiality only insofar as it can be thought of as separable into two things: namely that which initiates a change and that which is affected by it. Aristotle then says that the neediness of a potentiality is “for the same thing and in the same respect” as the corresponding potentiality. That is to say, every thing, which has a potential, has the corresponding need of that potential. Aristotle draws a distinction between rational and non-rational potentiality. A rational potentiality is a potentiality that involves reason. Aristotle says that every rational potentiality has potential for a pair of contraries, and that non-rational potential does not. For example, medical knowledge can produce either illness or health and a hot thing can only produce heat. The reason he gives for this is that a rational potential is a rational account and a rational account necessarily reveals the need of its object as well as its object. A non-rational potential cannot produce or receive contraries since contraries cannot occur in the same thing at once. A rational potentiality can produce contraries only because the contraries are not in a thing. Aristotle notes that a complete potentiality implies a partial potentiality, but that the converse is not generally true. Aristotle says th...
