On The Heavens   

will perceive what is greater. This, however, does not touch our

argument. The maximum may be determined either in the power or in

its object. The application of this is plain. Superior sight is

sight of the smaller body, but superior speed is that of the greater

body.



12



Having established these distinctions we car now proceed to the

sequel. If there are thing! capable both of being and of not being,

there must be some definite maximum time of their being and not being;

a time, I mean, during which continued existence is possible to them

and a time during which continued nonexistence is possible. And this

is true in every category, whether the thing is, for example, 'man',

or 'white', or 'three cubits long', or whatever it may be. For if

the time is not definite in quantity, but longer than any that can

be suggested and shorter than none, then it will be possible for one

and the same thing to exist for infinite time and not to exist for

another infinity. This, however, is impossible.

Let us take our start from this point. The impossible and the

false have not the same significance. One use of 'impossible' and

'possible', and 'false' and 'true', is hypothetical. It is impossible,

for instance, on a certain hypothesis that the triangle should have

its angles equal to two right angles, and on another the diagonal is

commensurable. But there are also things possible and impossible,

false and true, absolutely. Now it is one thing to be absolutely

false, and another thing to be absolutely impossible. To say that

you are standing when you are not standing is to assert a falsehood,

but not an impossibility. Similarly to say that a man who is playing

the harp, but not singing, is singing, is to say what is false but not

impossible. To say, however, that you are at once standing and

sitting, or that the diagonal is commensurable, is to say what is