Rational and Nonrational Potentiality

If what we have described is identical with the capable or convertible with it, evidently it cannot be true to say ’this is capable of being but will not be’, which would imply that the things incapable of being would on this showing vanish.

E.g. a man-one who did not take account of that which is incapable of being-were to say that the diagonal of the square is capable of being measured but will not be measured, because a thing may well be capable of being or coming to be, and yet not be or be about to be.

But from the premises this necessarily follows, that if we actually supposed that which is not, but is capable of being, to be or to have come to be, there will be nothing impossible in this;

But the result will be impossible, for the measuring of the diagonal is impossible. For the false and the impossible are not the same; that you are standing now is false, but that you should be standing is not impossible.

If, when A is real, B must be real, then, when A is possible, B also must be possible.

For if B need not be possible, there is nothing to prevent its not being possible. Now let A be supposed possible. Then, when A was possible, we agreed that nothing impossible followed if A were supposed to be real; and then B must of course be real. But we supposed B to be impossible.

Let it be impossible then. If, then, B is impossible, A also must be so. But the first was supposed impossible; therefore the second also is impossible. If, then, A is possible, B also will be possible, if they were so related that if A,is real, B must be real. If, then, A and B being thus related, B is not possible on this condition, and B will not be related as was supposed.

If when A is possible, B must be possible, then if A is real, B also must be real. For to say that B must be possible, if A is possible, means this, that if A is real both at the time when and in the way in which it was supposed capable of being real, B also must then and in that way be real.

Part 5

All potentialities are either:

• innate, like the senses
• come by practice, like the power of playing the flute, or
• by learning, like artistic power

Those which come by practice or by rational formula we must acquire by previous exercise. But this is not necessary with those which are not of this nature and which imply passivity.

That which is ‘capable’ is capable of something and at some time in some way.

Rational potentialities are those that can produce change according to a rational formula.

• This must be in a living thing

Nonrational potentialities are those that can produce change without a rational formula.

• This can be both in the living and in the lifeless.
• When the agent and the patient meet in the way appropriate to the potency in question, the one must act and the other be acted on,

but with the former kind of potency this is not necessary.

For the nonrational potencies are all productive of one effect each, but the rational produce contrary effects,

so that if they produced their effects necessarily they would produce contrary effects at the same time; but this is impossible.

The desire or will decides.

For whichever of two things the animal desires decisively, it will do, when it is present, and meets the passive object, in the way appropriate to the potency in question.

Therefore, everything which has a rational potency, when it desires that for which it has a potency and in the circumstances in which it has the potency, must do this.

It has the potentiality in question when the passive object is present and is in a certain state; if not it will not be able to act. (To add the qualification ‘if nothing external prevents it’ is not further necessary; for it has the potency on the terms on which this is a potency of acting, and it is this not in all circumstances but on certain conditions, among which will be the exclusion of external hindrances; for these are barred by some of the positive qualifications.)

Even if one has a rational wish or desire to do two things or contrary things at the same time, one will not do them.

for it is not on these terms that one has the potency for them, nor is it a potency of doing both at the same time, since one will do the things which it is a potency of doing, on the terms on which one has the potency.