The destruction of an actual part of a substantial existent...

The destruction of an actual part of a substantial existent and the appearance of another part in place of it, a clear instance of which is ‘generation and corruption’ such as the transformation of one component into another. The destruction of a potential part of a substance and the appearance of another potential part in place of it.

An instance of this posit is the substantial motion of bodies, which incessantly occurs with the destruction of one part and its replacement by another, parts which become existent by fluid existence and in which no actual part is to be found. In future lessons this will be further explained. The coming about of a new accident in a substantial subject, of which there are numerous instances.

The destruction of an accident without another accident taking its place, such as the fading of the color of a body and its becoming colorless. The destruction of an accident and the appearance of a different accident in its place, an instance of which is the succession of contrary accidents, such as the colors black and white. The destruction of an actual part of an accident.

An instance of this is the reduction of the number of something, according to those who consider number to be a real accident possessing actual parts. The addition of an actual part to an accident, such as the augmentation of the number of something according to the above-mentioned view. The destruction of a potential part of an accident and the appearance of another potential part, such as all accidental motion.

The attachment of one substantial existent to another, such as the attachment of the soul to the body and its coming to life. The detachment of one substantial existent from another, such as the death of an animal or human being. Observing the features of the above-mentioned types of change, it is clear that only the seventh and the thirteenth types are gradual and are examples of motion.

The other types must be considered instantaneous changes, for between the prior and latter conditions there is a specific boundary, and there is no temporal gap between them, although it is possible for each of the above-mentioned conditions to possess a kind of gradualness.

For example, a change in the temperature of water occurs gradually, although the transformation of water into steam occurs in a single moment, or a zygote gradually becomes complete, but a spirit becomes attached to it in a single moment.