Thomas Aquinas

“ But the particular distinctions of days and seasons and years, according as one day is hotter than another, one season than another, and one year than another, are due to certain particular movements of the stars: which movements may have had their beginning on the fourth day.
Reply to Objection 4: Light was given to the earth for the service of man, who, by reason of his soul, is nobler than the heavenly bodies. Nor is it untrue to say that a higher creature may be made for the sake of a lower, considered not in itself, but as ordained to the good of the universe. ”

“ From what has been said, then, it is clear that the heavenly bodies are not living beings in the same sense as plants and animals, and that if they are called so, it can only be equivocally. It will also be seen that the difference of opinion between those who affirm, and those who deny, that these bodies have life, is not a difference of things but of words. ”

“ There are, however, operations of the soul, which are not exercised through the medium of the body, though the body ministers, as it were, to their production. The intellect, for example, makes use of the phantasms derived from the bodily senses, and thus far is dependent on the body, although capable of existing apart from it. It is not, however, possible that the functions of nutrition, growth, and generation, through which the nutritive soul operates, can be exercised by the heavenly bodies, for such operations are incompatible with a body naturally incorruptible. ”

“ For the perfection of the heaven and the earth regards, seemingly, those things that belong to them intrinsically, but the adornment, those that are extrinsic, just as the perfection of a man lies in his proper parts and forms, and his adornment, in clothing or such like. Now just as distinction of certain things is made most evident by their local movement, as separating one from another; so the work of adornment is set forth by the production of things having movement in the heavens, and upon the earth. ”

“ 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. ”

“ No difficulty exists if we follow Augustine in holding the light made on the first day to be spiritual, and that made on this day to be corporeal. If, however, the light made on the first day is understood to be itself corporeal, then it must be held to have been produced on that day merely as light in general; and that on the fourth day the lights received a definite power to produce determinate effects. Thus we observe that the rays of the sun have one effect, those of the moon another, and so forth. ”

“ Now the nature and power of the soul are apprehended through its operation, which is to a certain extent its end. Yet for some of these operations, as sensation and nutrition, our body is a necessary instrument. Hence it is clear that the sensitive and nutritive souls must be united to a body in order to exercise their functions. ”

“ 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. ”