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