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14



There are six sorts of movement: generation, destruction,

increase, diminution, alteration, and change of place.

It is evident in all but one case that all these sorts of movement

are distinct each from each. Generation is distinct from

destruction, increase and change of place from diminution, and so

on. But in the case of alteration it may be argued that the process

necessarily implies one or other of the other five sorts of motion.

This is not true, for we may say that all affections, or nearly all,

produce in us an alteration which is distinct from all other sorts

of motion, for that which is affected need not suffer either

increase or diminution or any of the other sorts of motion. Thus

alteration is a distinct sort of motion; for, if it were not, the

thing altered would not only be altered, but would forthwith

necessarily suffer increase or diminution or some one of the other

sorts of motion in addition; which as a matter of fact is not the

case. Similarly that which was undergoing the process of increase or

was subject to some other sort of motion would, if alteration were not

a distinct form of motion, necessarily be subject to alteration

also. But there are some things which undergo increase but yet not

alteration. The square, for instance, if a gnomon is applied to it,

undergoes increase but not alteration, and so it is with all other

figures of this sort. Alteration and increase, therefore, are

distinct.

Speaking generally, rest is the contrary of motion. But the

different forms of motion have their own contraries in other forms;

thus destruction is the contrary of generation, diminution of

increase, rest in a place, of change of place. As for this last,

change in the reverse direction would seem to be most truly its