Potentiality Leads to Duality

Actuality is also better and more valuable than potentiality.

Everything that can do something can also do the contrary – it has both positive and negative potentialities at once.

This is seen in health and illness, rest and motion, building and destroying.

The capacity for contraries, then, is present at the same time.

But contraries cannot be present at the same time, and the actualities also cannot be present at the same time, e.g. health and illness.

Therefore, while the good must be one of them, the capacity is both alike, or neither; the actuality, then, is better.

Also in the case of bad things the end or actuality must be worse than the potency; for that which ‘can’ is both contraries alike. Clearly, then, the bad does not exist apart from bad things; for the bad is in its nature posterior to the potency.

Therefore we may also say that in the things which are from the beginning, i.e. in eternal things, there is nothing bad, nothing defective, nothing perverted (for perversion is something bad).

“It is an activity also that geometrical constructions are discovered; for we find them by dividing.

If the figures had been already divided, the constructions would have been obvious; but as it is they are present only potentially. Why are the angles of the triangle equal to two right angles? Because the angles about one point are equal to two right angles.

If, then, the line parallel to the side had been already drawn upwards, the reason would have been evident to any one as soon as he saw the figure. Why is the angle in a semicircle in all cases a right angle?

If three lines are equal the two which form the base, and the perpendicular from the centre-the conclusion is evident at a glance to one who knows the former proposition. Obviously, therefore, the potentially existing constructions are discovered by being brought to actuality; the reason is that the geometer’s thinking is an actuality; so that the potency proceeds from an actuality.

Therefore it is by making constructions that people come to know them (though the single actuality is later in generation than the corresponding potency). (See diagram.)