On Generation and corruption   

things are constantly being destroyed. For just as people speak of

'a passing-away' without qualification when a thing has passed into

what is imperceptible and what in that sense 'is not', so also they

speak of 'a coming-to-be out of a not-being' when a thing emerges from

an imperceptible. Whether, therefore, the substratum is or is not

something, what comes-tobe emerges out of a 'not-being': so that a

thing comes-to-be out of a not-being' just as much as it

'passes-away into what is not'. Hence it is reasonable enough that

coming-to-be should never fail. For coming-to-be is a passing-away

of 'what is not' and passing-away is a coming to-be of 'what is not'.

But what about that which 'is' not except with a qualification? Is

it one of the two contrary poles of the chang-e.g. Earth (i.e. the

heavy) a 'not-being', but Fire (i.e. the light) a 'being'? Or, on

the contrary, does what is 'include Earth as well as Fire, whereas

what is not' is matter-the matter of Earth and Fire alike? And

again, is the matter of each different? Or is it the same, since

otherwise they would not come-to-be reciprocally out of one another,

i.e. contraries out of contraries? For these things-Fire, Earth,

Water, Air-are characterized by 'the contraries'.

Perhaps the solution is that their matter is in one sense the

same, but in another sense different. For that which underlies them,

whatever its nature may be qua underlying them, is the same: but its

actual being is not the same. So much, then, on these topics.

4



Next we must state what the difference is between coming-to-be and

'alteration'-for we maintain that these changes are distinct from

one another.

Since, then, we must distinguish (a) the substratum, and (b) the

property whose nature it is to be predicated of the substratum; and

since change of each of these occurs; there is 'alteration' when the

substratum is perceptible and persists, but changes in its own