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 primary 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 “efficient 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,[399] “appears to hold the chief place among natural causes which we signify under this expression, ‘cujus gratiâ’—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 the reasons and causes of what he does, and adds why he does it; although that cause, ‘cujus gratiâ,’ and the reason ‘for the sake of the good and fair,’ are joined rather to the works of nature than to those of art.”
“The end,” he elsewhere says,[400] “is this ‘cujus gratiâ’ (for whose sake), as health is the thing for the sake of which we walk. For why does a man walk? We answer, for the sake of his health; and when we have thus said, we think we have given a ‘cause;’ and whatever else is further interposed, by means of another agent, is done for the sake of this end, as dieting, or purging, or drugs, or instruments, are all for the sake of health; for all these are for the sake of the end.” Again, “It is our business always to seek the primary cause of everything. For instance, a man builds a house because he is a builder, but he is a builder by reason of the art of building; this then (the art) is a prior cause; and so in all things.” Hence it is that he asserts[401] “that the cause which first moves, and in which the ‘reason’ and ‘form’ lie, is greater and more divine than the ‘material cause.’”
In all natural generation, therefore, both the “matter” out of which and the “efficient cause” by which (namely, A, the thing which is moved, and B, the thing moving) are alike for the sake of the animal begotten or to be begotten; for that which moves and is not itself moved, viz. C, is in (inest) both. For both those (viz. A and B) are at the same time capable of motion, and are moreover moved, viz. the thing fecundating, B, (which both moves and is moved) and the thing fecundated, A, the “matter,” viz. or ovum, which is moved and changed only. Wherefore if no moveable thing is actually moved, unless the thing which moves is present, so neither will “matter” be moved, nor the “efficient” effect anything, unless the first moving cause be in some way present; and this is the “form” or “species” which is without matter, and is the prime cause. “For the efficient and generating,” according to Aristotle,[402] “in so far as they are so, belong to that which is effected and generated.” The following syllogism, therefore, may be framed out of these first and necessary predicates:
Whenever B is actually in existence, C also is actually in existence (i. e. moving in some way).
Whenever A is actually in existence, B is also in actual existence.
Therefore whenever A is in actual existence, C is also in actual existence.
Natural and artificial generation take place after the same manner.[403] Both are instituted for the sake of something further, and by a kind of providence both direct themselves to a proposed end;—both too are first moved by some “form” conceived without matter, and are the products of this conception. The brain is the organ of one kind of conception (for in the soul, the organ of which is the brain, art, without the intervention of matter, is the “reason” or first cause of the work), the uterus or ovum of the other.
The “conception,” therefore, of the uterus or the ovum resembles, at least in some sort, the conception of the brain itself, and in a similar way does the “end” inhere in both. For the “species” or “form” of the chick is in the uterus or ovum without the intervention of matter, just as the “reason” of his work is in the artist, e. g. the “reason” of the house in the brain of the builder.
But since the phrase “to be in” is perhaps equivocal, and things are said to be coexistent in various senses, I affirm, further, and say, that the “species” and immaterial “form” of the future chick are, in some sort, the cause of the impregnation or fecundation of the uterus, because after intercourse no corporeal substance can be found within that organ.