On Generation and corruption   

more or less 'substantial', or upon whether it is more or less

perceptible.

(ii) But why are some things said to 'come to-be' without

qualification, and others only to 'come-to-be-so-and-so', in cases

different from the one we have been considering where two things

come-to-be reciprocally out of one another? For at present we have

explained no more than this:-why, when two things change

reciprocally into one another, we do not attribute coming-to-be and

passing-away uniformly to them both, although every coming-to-be is

a passing-away of something else and every passing-away some other

thing's coming-to-be. But the question subsequently formulated

involves a different problem-viz. why, although the learning thing

is said to 'come-to-be-learned' but not to 'come-tobe' without

qualification, yet the growing thing is said to 'come-to-be'.

The distinction here turns upon the difference of the Categories.

For some things signify a this somewhat, others a such, and others a

so-much. Those things, then, which do not signify substance, are not

said to 'come-to-be' without qualification, but only to

'come-to-be-so-and-so'. Nevertheless, in all changing things alike, we

speak of 'coming-to-be' when the thing comes-to-be something in one of

the two Columns-e.g. in Substance, if it comes-to-be Fire but not if

it comes-to-be Earth; and in Quality, if it comes-to-be learned but

not when it comes-to-be ignorant.

We have explained why some things come to-be without

qualification, but not others both in general, and also when the

changing things are substances and nothing else; and we have stated

that the substratum is the material cause of the continuous occurrence

of coming to-be, because it is such as to change from contrary to

contrary and because, in substances, the coming-to-be of one thing

is always a passing-away of another, and the passing-away of one thing

is always another's coming-to-be. But there is no need even to discuss

the other question we raised-viz. why coming-to-be continues though