Book 9
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.
10
Similarly men possess the art of building in order that they may build, and the power of speculation that they may speculate; they do not speculate in order that they may have the power of speculation—except those who are learning by practice; and they do not really speculate, but only in a limited sense, or about a subject about which they have no desire to speculate.
10
Further, matter exists potentially, because it may attain to the form; but when it exists actually, it is then in the form. The same applies in all other cases, including those where the end is motion.
11
Hence, just as teachers think that they have achieved their end when they have exhibited their pupil performing, so it is with nature. For if this is not so, it will be another case of Pauson’s HermesProbably a trick picture of some kind. So Pauson is said to have painted a picture of a horse galloping which when inverted showed the horse rolling on its back. Cf. Aelian, Var. Hist. 14.15; Lucian, Demosth. Enc. 24; Plut. Moralia, 396e; Pfuhl, Malerei und Zeichnung der Griechen, 763.; it will be impossible to say whether the knowledge is in the pupil or outside him, as in the case of the Hermes. For the activity is the end, and the actuality is the activity; hence the term actuality is derived from activity, and tends to have the meaning of complete reality.
