Capability and Potentiality and Actuality

The Megaric school says that a thing ‘can’ act only when it is acting. When it is not acting, it ‘cannot’ act.

• For example, he who is not building cannot build.
• Only one who is building can build when he is building.

A man will not be a builder unless he is building.

If so, then it is impossible to have such arts if one has not learnt them before.

• It is then impossible not to have them if one has not lost them before

Knowledge can be lost by:

• forgetfulness or
• some accident
• time

Knowledge cannot be lost by the the destruction of the object, for that lasts forever.

A man will not have the art when he has ceased to use it. Yet he may immediately build again.

How then will he have got the art?

This is similar with regard to lifeless things.

Nothing will be cold, hot, sweet, or perceptible at all if people are not perceiving it.

• The upholders of this view will have to maintain the doctrine of Protagoras.

But nothing will even have perception if it is not perceiving, i.e. exercising its perception.

If, then, that is blind which has not sight though it would naturally have it, when it would naturally have it and when it still exists, the same people will be blind many times in the day-and deaf too.

If that which is deprived of potentiality is incapable, that which is not happening will be incapable of happening.

But he who says of that which is incapable of happening either that it is or that it will be will say what is untrue; for this is what incapacity meant.

Therefore, these views do away with both movement and becoming.

We cannot say:

• that which stands will always stand.
• that which sits will always sit.

This is because:

• if it is sitting then it will not get up
• that which cannot get up will be incapable of getting up

Therefore, potentiality and actuality are different.

But these views make potentiality and actuality the same.

So it is possible that a thing may be:

• capable of being and not be
• capable of not being and yet be

Similarly, with the other kinds of predicate.

It may be capable of walking and yet not walk, or capable of not walking and yet walk.

A thing cam do something if there will be nothing impossible in its having the actuality of that of which it is said to have the capacity.

• If a thing can sit, there will be nothing impossible in its actually sitting.
• If it can move or be moved, or stand

We connect ‘actuality’ with ‘complete reality’. It has been extended from movements to other things.

Actuality in the strict sense is thought to be identical with movement.

And so people do not assign movement to non-existent things, though they do assign some other predicates.

• E.g. they say that non-existent things are objects of thought and desire, but not that they are moved.

This because, while ex hypothesi they do not actually exist, they would have to exist actually if they were moved.

For of non-existent things some exist potentially; but they do not exist, because they do not exist in complete reality.