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forms, since their form perfects their matter entirely, which is not in potentiality to other forms; whereas a soul does not do this. Also as regards movement the power that moves the heavenly bodies is of a nobler kind.
Reply Obj. 3: Since the heavenly body is a mover moved, it is of the nature of an instrument, which acts in virtue of the agent: and therefore since this agent is a living substance the heavenly body can impart life in virtue of that agent.
Reply Obj. 4: The movements of the heavenly bodies are natural, not on account of their active principle, but on account of their passive principle; that is to say, from a certain natural aptitude for being moved by an intelligent power.
Reply Obj. 5: The heaven is said to move itself in as far as it is compounded of mover and moved; not by the union of the mover, as the form, with the moved, as the matter, but by contact with the motive power, as we have said. So far, then, the principle that moves it may be called intrinsic, and consequently its movement natural with respect to that active principle; just as we say that voluntary movement is natural to the animal as animal (Phys. viii, text. 27).
QUESTION 71
ON THE WORK OF THE FIFTH DAY (In One Article)
We must next consider the work of the fifth day.
Objection 1: It would seem that this work is not fittingly described. For the waters produce that which the power of water suffices to produce. But the power of water does not suffice for the production of every kind of fishes and birds since we find that many of them are generated from seed. Therefore the words, "Let the waters bring forth the creeping creature having life, and the fowl that may fly over the earth," do not