ON CONCEPTION. 583
convertible into the cluck, and is in fact the chicken in posse. Let B be that which fecundates the egg, and thus distinguishes it from an unfruitful egg, i. e. the " efficient cause" of the chick, or that which puts the egg in motion, and converts it into a chick. And let C be the chick, or " final cause," for the sake of which both the egg and that which fecundates the egg exist, the actual chick, namely, or "reason" why the chick is.
Now we take for granted, as demonstrated by Aristotle, 1 that every prime mover is " combined with" that which is moved by it. And these things are more particularly said by him to be " together" which are generated or produced at the same moment of time : thus that which moves and that which is moved are actually together, and where one is there the other is also ; for it is evident that when the effect is present the cause must be so too.
Whenever, then, A (i. e. the fecundated egg) is actually in being, B (i. e. the internal moving and "efficient" or fecundating cause) is also actually in being. But when B is actually in being, C also (i. e. the immaterial " form" of the chick) must, at least in some sort, be existing too. For B is the internal efficient cause of the chick, that, namely, which alters A (the egg) into C (the "reason" why the chick is). Since, then, everything which moves coexists with that which is moved by it, and every cause with its effect, it follows that C coexists with B ; for the " final cause," both in nature and art, is pri- mary to all other causes, since it moves, and is not itself moved; but the " efficient" moves, because it is impelled by the " final cause." There inheres, in some way or other, in every "effi- cient cause" a ratio finis (a final cause), and by this the efficient, co-operating with Providence, is moved.
The authority of Aristotle is clearly on my side : " That," he says,2 " appears to hold the chief place among natural causes which we signify under this expression, ' cujus gratia/ for whose sake. For this is the 'reason/ but the 'reason' is the chief thing, as well in artificial as in natural subjects. For when a physician explains what health is, either by definition or description, or a workman a house, he is accustomed to give
1 Plusiologia, lib. vii, cap. 3. 3 De Part. Anirn. lib. i, cap. 1.
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