As, then, no change takes place in themselves, these cannot be
said to be capable of admitting contrary qualities.

But it is by reason of the modification which takes place within
the substance itself that a substance is said to be capable of
admitting contrary qualities; for a substance admits within
itself either disease or health, whiteness or blackness. It is in
this sense that it is said to be capable of admitting contrary
qualities.

To sum up, it is a distinctive mark of substance, that, while
remaining numerically one and the same, it is capable of
admitting contrary qualities, the modification taking place
through a change in the substance itself.

Let these remarks suffice on the subject of substance.

Part 6

Quantity is either discrete or continuous. Moreover, some
quantities are such that each part of the whole has a relative
position to the other parts: others have within them no such
relation of part to part.

Instances of discrete quantities are number and speech; of
continuous, lines, surfaces, solids, and, besides these, time and
place.

In the case of the parts of a number, there is no common boundary
at which they join. For example: two fives make ten, but the two