Objection 1: It would seem that the lights ought not to have been produced on the fourth day. For the heavenly luminaries are by nature incorruptible bodies: wherefore their matter cannot exist without their form. But as their matter was produced in the work of creation, before there was any day, so therefore were their forms. It follows, then, that the lights were not produced on the fourth day.

Objection 2: Further, the luminaries are, as it were, vessels of light. But light was made on the first day. The luminaries, therefore, should have been made on the first day, not on the fourth.

Objection 3: Further, the lights are fixed in the firmament, as plants are fixed in the earth. For, the Scripture says: "He set them in the firmament." But plants are described as produced when the earth, to which they are attached, received its form. The lights, therefore, should have been produced at the same time as the firmament, that is to say, on the second day.

Objection 4: Further, plants are an effect of the sun, moon, and other heavenly bodies. Now, cause precedes effect in the order of nature. The lights, therefore, ought not to have been produced on the fourth day, but on the third day.

Objection 5: Further, as astronomers say, there are many stars larger than the moon. Therefore the sun and the moon alone are not correctly described as the "two great lights."

On the contrary, Suffices the authority of Scripture.

I answer that, In recapitulating the Divine works, Scripture says (Gn. 2:1): "So the heavens and the earth were finished and all the furniture of them," thereby indicating that the work was threefold. In the first work, that of "creation," the heaven and the earth were produced, but as yet without form. In the second, or work of "distinction," the heaven and the earth were perfected, either by adding substantial form to formless matter, as Augustine holds (Gen. ad lit. ii, 11), or by giving them the order and beauty due to them, as other holy writers suppose. To these two works is added the work of adornment, which is distinct from perfect. 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. But it has been stated above (Question [69], Article [1]), that three things are recorded as created, namely, the heaven, the water, and the earth; and these three received their form from the three days' work of distinction, so that heaven was formed on the first day; on the second day the waters were separated; and on the third day, the earth was divided into sea and dry land. So also is it in the work of adornment; on the first day of this work, which is the fourth of creation, are produced the lights, to adorn the heaven by their movements; on the second day, which is the fifth, birds and fishes are called into being, to make beautiful the intermediate element, for they move in air and water, which are here taken as one; while on the third day, which is the sixth, animals are brought forth, to move upon the earth and adorn it. It must also here be noted that Augustine's opinion (Gen. ad lit. v, 5) on the production of lights is not at variance with that of other holy writers, since he says that they were made actually, and not merely virtually, for the firmament has not the power of producing lights, as the earth has of producing plants. Wherefore Scripture does not say: "Let the firmament produce lights," though it says: "Let the earth bring forth the green herb."

Reply to Objection 1: In Augustine's opinion there is no difficulty here; for he does not hold a succession of time in these works, and so there was no need for the matter of the lights to exist under another form. Nor is there any difficulty in the opinion of those who hold the heavenly bodies to be of the nature of the four elements, for it may be said that they were formed out of matter already existing, as animals and plants were formed. For those, however, who hold the heavenly bodies to be of another nature from the elements, and naturally incorruptible, the answer must be that the lights were substantially created at the beginning, but that their substance, at first formless, is formed on this day, by receiving not its substantial form, but a determination of power. As to the fact that the lights are not mentioned as existing from the beginning, but only as made on the fourth day, Chrysostom (Hom. vi in Gen.) explains this by the need of guarding the people from the danger of idolatry: since the lights are proved not to be gods, by the fact that they were not from the beginning.

Reply to Objection 2: 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. Hence, speaking of such a determination of power, Dionysius (Div. Nom. iv) says that the sun's light which previously was without form, was formed on the fourth day.

Reply to Objection 3: According to Ptolemy the heavenly luminaries are not fixed in the spheres, but have their own movement distinct from the movement of the spheres. Wherefore Chrysostom says (Hom. vi in Gen.) that He is said to have set them in the firmament, not because He fixed them there immovably, but because He bade them to be there, even as He placed man in Paradise, to be there. In the opinion of Aristotle, however, the stars are fixed in their orbits, and in reality have no other movement but that of the spheres; and yet our senses perceive the movement of the luminaries and not that of the spheres (De Coel. ii, text. 43). But Moses describes what is obvious to sense, out of condescension to popular ignorance, as we have already said (Question [67], Article [4]; Question [68], Article [3]). The objection, however, falls to the ground if we regard the firmament made on the second day as having a natural distinction from that in which the stars are placed, even though the distinction is not apparent to the senses, the testimony of which Moses follows, as stated above (De Coel. ii, text. 43). For although to the senses there appears but one firmament; if we admit a higher and a lower firmament, the lower will be that which was made on the second day, and on the fourth the stars were fixed in the higher firmament.

Reply to Objection 4: In the words of Basil (Hom. v in Hexaem.), plants were recorded as produced before the sun and moon, to prevent idolatry, since those who believe the heavenly bodies to be gods, hold that plants originate primarily from these bodies. Although as Chrysostom remarks (Hom. vi in Gen.), the sun, moon, and stars cooperate in the work of production by their movements, as the husbandman cooperates by his labor.

Reply to Objection 5: As Chrysostom says, the two lights are called great, not so much with regard to their dimensions as to their influence and power. For though the stars be of greater bulk than the moon, yet the influence of the moon is more perceptible to the senses in this lower world. Moreover, as far as the senses are concerned, its apparent size is greater.

Objection 1: It would seem that the cause assigned for the production of the lights is not reasonable. For it is said (Jer. 10:2): "Be not afraid of the signs of heaven, which the heathens fear." Therefore the heavenly lights were not made to be signs.

Objection 2: Further, sign is contradistinguished from cause. But the lights are the cause of what takes place upon the earth. Therefore they are not signs.

Objection 3: Further, the distinction of seasons and days began from the first day. Therefore the lights were not made "for seasons, and days, and years," that is, in order to distinguish them.

Objection 4: Further, nothing is made for the sake of that which is inferior to itself, "since the end is better than the means" (Topic. iii). But the lights are nobler than the earth. Therefore they were not made "to enlighten it."

Objection 5: Further, the new moon cannot be said "to rule the night." But such it probably did when first made; for men begin to count from the new moon. The moon, therefore, was not made "to rule the night."

On the contrary, Suffices the authority of Scripture.

I answer that, As we have said above (Question [65], Article [2]), a corporeal creature can be considered as made either for the sake of its proper act, or for other creatures, or for the whole universe, or for the glory of God. Of these reasons only that which points out the usefulness of these things to man, is touched upon by Moses, in order to withdraw his people from idolatry. Hence it is written (Dt. 4:19): "Lest perhaps lifting up thy eyes to heaven, thou see the sun and the moon and all the stars of heaven, and being deceived by error thou adore and serve them, which the Lord thy God created for the service of all nations." Now, he explains this service at the beginning of Genesis as threefold. First, the lights are of service to man, in regard to sight, which directs him in his works, and is most useful for perceiving objects. In reference to this he says: "Let them shine in the firmament and give life to the earth." Secondly, as regards the changes of the seasons, which prevent weariness, preserve health, and provide for the necessities of food; all of which things could not be secured if it were always summer or winter. In reference to this he says: "Let them be for seasons, and for days, and years." Thirdly, as regards the convenience of business and work, in so far as the lights are set in the heavens to indicate fair or foul weather, as favorable to various occupations. And in this respect he says: "Let them be for signs."

Reply to Objection 1: The lights in the heaven are set for signs of changes effected in corporeal creatures, but not of those changes which depend upon the free-will.

Reply to Objection 2: We are sometimes brought to the knowledge of hidden effects through their sensible causes, and conversely. Hence nothing prevents a sensible cause from being a sign. But he says "signs," rather than "causes," to guard against idolatry.

Reply to Objection 3: The general division of time into day and night took place on the first day, as regards the diurnal movement, which is common to the whole heaven and may be understood to have begun on that first day. 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.

Reply to Objection 5: When the moon is at its perfection it rises in the evening and sets in the morning, and thus it rules the night, and it was probably made in its full perfection as were plants yielding seed, as also were animals and man himself. For although the perfect is developed from the imperfect by natural processes, yet the perfect must exist simply before the imperfect. Augustine, however (Gen. ad lit. ii), does not say this, for he says that it is not unfitting that God made things imperfect, which He afterwards perfected.

Objection 1: It would seem that the lights of heaven are living beings. For the nobler a body is, the more nobly it should be adorned. But a body less noble than the heaven, is adorned with living beings, with fish, birds, and the beasts of the field. Therefore the lights of heaven, as pertaining to its adornment, should be living beings also.

Objection 2: Further, the nobler a body is, the nobler must be its form. But the sun, moon, and stars are nobler bodies than plants or animals, and must therefore have nobler forms. Now the noblest of all forms is the soul, as being the first principle of life. Hence Augustine (De Vera Relig. xxix) says: "Every living substance stands higher in the order of nature than one that has not life." The lights of heaven, therefore, are living beings.

Objection 3: Further, a cause is nobler than its effect. But the sun, moon, and stars are a cause of life, as is especially evidenced in the case of animals generated from putrefaction, which receive life from the power of the sun and stars. Much more, therefore, have the heavenly bodies a living soul.

Objection 4: Further, the movement of the heaven and the heavenly bodies are natural (De Coel. i, text. 7,8): and natural movement is from an intrinsic principle. Now the principle of movement in the heavenly bodies is a substance capable of apprehension, and is moved as the desirer is moved by the object desired (Metaph. xii, text. 36). Therefore, seemingly, the apprehending principle is intrinsic to the heavenly bodies: and consequently they are living beings.

Objection 5: Further, the first of movables is the heaven. Now, of all things that are endowed with movement the first moves itself, as is proved in Phys. viii, text. 34, because, what is such of itself precedes that which is by another. But only beings that are living move themselves, as is shown in the same book (text. 27). Therefore the heavenly bodies are living beings.

On the contrary, Damascene says (De Fide Orth. ii), "Let no one esteem the heavens or the heavenly bodies to be living things, for they have neither life nor sense."

I answer that, Philosophers have differed on this question. Anaxagoras, for instance, as Augustine mentions (De Civ. Dei xviii, 41), "was condemned by the Athenians for teaching that the sun was a fiery mass of stone, and neither a god nor even a living being." On the other hand, the Platonists held that the heavenly bodies have life. Nor was there less diversity of opinion among the Doctors of the Church. It was the belief of Origen (Peri Archon i) and Jerome that these bodies were alive, and the latter seems to explain in that sense the words (Eccles. 1:6), "The spirit goeth forward, surveying all places round about." But Basil (Hom. iii, vi in Hexaem.) and Damascene (De Fide Orth. ii) maintain that the heavenly bodies are inanimate. Augustine leaves the matter in doubt, without committing himself to either theory, though he goes so far as to say that if the heavenly bodies are really living beings, their souls must be akin to the angelic nature (Gen. ad lit. ii, 18; Enchiridion lviii).

In examining the truth of this question, where such diversity of opinion exists, we shall do well to bear in mind that the union of soul and body exists for the sake of the soul and not of the body; for the form does not exist for the matter, but the matter for the form. 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. 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. Equally impossible is it that the functions of the sensitive soul can appertain to the heavenly body, since all the senses depend on the sense of touch, which perceives elemental qualities, and all the organs of the senses require a certain proportion in the admixture of elements, whereas the nature of the heavenly bodies is not elemental. It follows, then, that of the operations of the soul the only ones left to be attributed to the heavenly bodies are those of understanding and moving; for appetite follows both sensitive and intellectual perception, and is in proportion thereto. But the operations of the intellect, which does not act through the body, do not need a body as their instrument, except to supply phantasms through the senses. Moreover, the operations of the sensitive soul, as we have seen, cannot be attributed to the heavenly bodies. Accordingly, the union of a soul to a heavenly body cannot be for the purpose of the operations of the intellect. It remains, then, only to consider whether the movement of the heavenly bodies demands a soul as the motive power, not that the soul, in order to move the heavenly body, need be united to the latter as its form; but by contact of power, as a mover is united to that which he moves. Wherefore Aristotle (Phys. viii, text. 42,43), after showing that the first mover is made up of two parts, the moving and the moved, goes on to show the nature of the union between these two parts. This, he says, is effected by contact which is mutual if both are bodies; on the part of one only, if one is a body and the other not. The Platonists explain the union of soul and body in the same way, as a contact of a moving power with the object moved, and since Plato holds the heavenly bodies to be living beings, this means nothing else but that substances of spiritual nature are united to them, and act as their moving power. A proof that the heavenly bodies are moved by the direct influence and contact of some spiritual substance, and not, like bodies of specific gravity, by nature, lies in the fact that whereas nature moves to one fixed end which having attained, it rests; this does not appear in the movement of heavenly bodies. Hence it follows that they are moved by some intellectual substances. Augustine appears to be of the same opinion when he expresses his belief that all corporeal things are ruled by God through the spirit of life (De Trin. iii, 4).

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.

Reply to Objection 1: Certain things belong to the adornment of the universe by reason of their proper movement; and in this way the heavenly luminaries agree with others that conduce to that adornment, for they are moved by a living substance.

Reply to Objection 2: One being may be nobler than another absolutely, but not in a particular respect. While, then, it is not conceded that the souls of heavenly bodies are nobler than the souls of animals absolutely it must be conceded that they are superior to them with regard to their respective 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 to Objection 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 to Objection 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 to Objection 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).