Book 9
7
This was the origin of the sophists’ quibble that a man who does not know a given science will be doing that which is the object of that science, because the learner does not know the science. But since something of that which is being generated is already generated, and something of that which is being moved as a whole is already moved (this is demonstrated in our discussion on MotionAristot. Physics, 6.6.), presumably the learner too must possess something of the science.
8
At any rate from this argument it is clear that actuality is prior to potentiality in this sense too, i.e. in respect of generation and time.
8
But it is also prior in substantiality; (a) because things which are posterior in generation are prior in form and substantiality; e.g., adult is prior to child, and man to semen, because the one already possesses the form, but the other does not;
9
and (b) because everything which is generated moves towards a principle, i.e. its end . For the object of a thing is its principle; and generation has as its object the end . And the actuality is the end, and it is for the sake of this that the potentiality is acquired; for animals do not see in order that they may have sight, but have sight in order that they may see.
