[I.q.67.a.1.arg.1] It would seem that "light" is used in its proper sense in spiritual things. For Augustine says (Gen. ad lit. iv, 28) that "in spiritual things light is better and surer: and that Christ is not called Light in the same sense as He is called the Stone; the former is to be taken literally, and the latter metaphorically."

[I.q.67.a.1.arg.2] Further, Dionysius (Div. Nom. iv) includes Light among the intellectual names of God. But such names are used in their proper sense in spiritual things. Therefore light is used in its proper sense in spiritual matters.

[I.q.67.a.1.arg.3] Further, the Apostle says (Ephesians 5:13): "All that is made manifest is light." But to be made manifest belongs more properly to spiritual things than to corporeal. Therefore also does light.

[I.q.67.a.1.sc] Ambrose says (De Fide ii) that "Splendor" is among those things which are said of God metaphorically.

[I.q.67.a.1.co] Any word may be used in two ways--that is to say, either in its original application or in its more extended meaning. This is clearly shown in the word "sight," originally applied to the act of the sense, and then, as sight is the noblest and most trustworthy of the senses, extended in common speech to all knowledge obtained through the other senses. Thus we say, "Seeing how it tastes," or "smells," or "burns. "Further, sight is applied to knowledge obtained through the intellect, as in those words: "Blessed are the clean of heart, for they shall see God" (Matthew 5:8). And thus it is with the word light. In its primary meaning it signifies that which makes manifest to the sense of sight; afterwards it was extended to that which makes manifest to cognition of any kind. If, then, the word is taken in its strict and primary meaning, it is to be understood metaphorically when applied to spiritual things, as Ambrose says (De Fide ii). But if taken in its common and extended use, as applied to manifestation of every kind, it may properly be applied to spiritual things.

The answer to the objections will sufficiently appear from what has been said.

[I.q.67.a.2.arg.1] It would seem that light is a body. For Augustine says (De Lib. Arb. iii, 5) that "light takes the first place among bodies."Therefore light is a body.

[I.q.67.a.2.arg.2] Further, the Philosopher says (Topic. v, 2) that "light is a species of fire." But fire is a body, and therefore so is light.

[I.q.67.a.2.arg.3] Further, the powers of movement, intersection, reflection, belong properly to bodies; and all these are attributes of light and its rays. Moreover, different rays of light, as Dionysius says (Div. Nom. ii) are united and separated, which seems impossible unless they are bodies. Therefore light is a body.

[I.q.67.a.2.sc] Two bodies cannot occupy the same place simultaneously. But this is the case with light and air. Therefore light is not a body.

[I.q.67.a.2.co] Light cannot be a body, for three evident reasons.

First, on the part of place. For the place of any one body is different from that of any other, nor is it possible, naturally speaking, for any two bodies of whatever nature, to exist simultaneously in the same place; since contiguity requires distinction of place.

The second reason is from movement. For if light were a body, its diffusion would be the local movement of a body. Now no local movement of a body can be instantaneous, as everything that moves from one place to another must pass through the intervening space before reaching the end: whereas the diffusion of light is instantaneous. Nor can it be argued that the time required is too short to be perceived; for though this may be the case in short distances, it cannot be so in distances so great as that which separates the East from the West. Yet as soon as the sun is at the horizon, the whole hemisphere is illuminated from end to end. It must also be borne in mind on the part of movement that whereas all bodies have their natural determinate movement, that of light is indifferent as regards direction, working equally in a circle as in a straight line. Hence it appears that the diffusion of light is not the local movement of a body.

The third reason is from generation and corruption. For if light were a body, it would follow that whenever the air is darkened by the absence of the luminary, the body of light would be corrupted, and its matter would receive a new form. But unless we are to say that darkness is a body, this does not appear to be the case. Neither does it appear from what matter a body can be daily generated large enough to fill the intervening hemisphere. Also it would be absurd to say that a body of so great a bulk is corrupted by the mere absence of the luminary. And should anyone reply that it is not corrupted, but approaches and moves around with the sun, we may ask why it is that when a lighted candle is obscured by the intervening object the whole room is darkened? It is not that the light is condensed round the candle when this is done, since it burns no more brightly then than it burned before.

Since, therefore, these things are repugnant, not only to reason, but to common sense, we must conclude that light cannot be a body.

[I.q.67.a.2.ad.1] Augustine takes light to be a luminous body in act--in other words, to be fire, the noblest of the four elements.

[I.q.67.a.2.ad.2] Aristotle pronounces light to be fire existing in its own proper matter: just as fire in aerial matter is "flame," or in earthly matter is "burning coal." Nor must too much attention be paid to the instances adduced by Aristotle in his works on logic, as he merely mentions them as the more or less probable opinions of various writers.

[I.q.67.a.2.ad.3] All these properties are assigned to light metaphorically, and might in the same way be attributed to heat. For because movement from place to place is naturally first in the order of movement as is proved Phys. viii, text. 55, we use terms belonging to local movement in speaking of alteration and movement of all kinds. For even the word distance is derived from the idea of remoteness of place, to that of all contraries, as is said Metaph. x, text. 13.

[I.q.67.a.3.arg.1] It would seem that light is not a quality. For every quality remains in its subject, though the active cause of the quality be removed, as heat remains in water removed from the fire. But light does not remain in the air when the source of light is withdrawn. Therefore light is not a quality.

[I.q.67.a.3.arg.2] Further, every sensible quality has its opposite, as cold is opposed to heat, blackness to whiteness. But this is not the case with light since darkness is merely a privation of light. Light therefore is not a sensible quality.

[I.q.67.a.3.arg.3] Further, a cause is more potent than its effect. But the light of the heavenly bodies is a cause of substantial forms of earthly bodies, and also gives to colors their immaterial being, by making them actually visible. Light, then, is not a sensible quality, but rather a substantial or spiritual form.

[I.q.67.a.3.sc] Damascene (De Fide Orth. i) says that light is a species of quality.

[I.q.67.a.3.co] Some writers have said that the light in the air has not a natural being such as the color on a wall has, but only an intentional being, as a similitude of color in the air. But this cannot be the case for two reasons.

First, because light gives a name to the air, since by it the air becomes actually luminous. But color does not do this, for we do not speak of the air as colored.

Secondly, because light produces natural effects, for by the rays of the sun bodies are warmed, and natural changes cannot be brought about by mere intentions.

Others have said that light is the sun's substantial form, but this also seems impossible for two reasons. First, because substantial forms are not of themselves objects of the senses; for the object of the intellect is what a thing is, as is said De Anima iii, text. 26: whereas light is visible of itself. In the second place, because it is impossible that what is the substantial form of one thing should be the accidental form of another; since substantial forms of their very nature constitute species: wherefore the substantial form always and everywhere accompanies the species. But light is not the substantial form of air, for if it were, the air would be destroyed when light is withdrawn. Hence it cannot be the substantial form of the sun.

We must say, then, that as heat is an active quality consequent on the substantial form of fire, so light is an active quality consequent on the substantial form of the sun, or of another body that is of itself luminous, if there is any such body. A proof of this is that the rays of different stars produce different effects according to the diverse natures of bodies.

[I.q.67.a.3.ad.1] Since quality is consequent upon substantial form, the mode in which the subject receives a quality differs as the mode differs in which a subject receives a substantial form. For when matter receives its form perfectly, the qualities consequent upon the form are firm and enduring; as when, for instance, water is converted into fire. When, however, substantial form is received imperfectly, so as to be, as it were, in process of being received, rather than fully impressed, the consequent quality lasts for a time but is not permanent; as may be seen when water which has been heated returns in time to its natural state. But light is not produced by the transmutation of matter, as though matter were in receipt of a substantial form, and light were a certain inception of substantial form. For this reason light disappears on the disappearance of its active cause.

[I.q.67.a.3.ad.2] It is accidental to light not to have a contrary, forasmuch as it is the natural quality of the first corporeal cause of change, which is itself removed from contrariety.

[I.q.67.a.3.ad.3] As heat acts towards perfecting the form of fire, as an instrumental cause, by virtue of the substantial form, so does light act instrumentally, by virtue of the heavenly bodies, towards producing substantial forms; and towards rendering colors actually visible, inasmuch as it is a quality of the first sensible body.

[I.q.67.a.4.arg.1] It would seem that the production of light is not fittingly assigned to the first day. For light, as stated above (Article 3), is a quality. But qualities are accidents, and as such should have, not the first, but a subordinate place. The production of light, then, ought not to be assigned to the first day.

[I.q.67.a.4.arg.2] Further, it is light that distinguishes night from day, and this is effected by the sun, which is recorded as having been made on the fourth day. Therefore the production of light could not have been on the first day.

[I.q.67.a.4.arg.3] Further, night and day are brought about by the circular movement of a luminous body. But movement of this kind is an attribute of the firmament, and we read that the firmament was made on the second day. Therefore the production of light, dividing night from day, ought not to be assigned to the first day.

[I.q.67.a.4.sc] That without which there could not be day, must have been made on the first day. But there can be no day without light. Therefore light must have been made on the first day.

[I.q.67.a.4.co] There are two opinions as to the production of light. Augustine seems to say (De Civ. Dei xi, 9,33) that Moses could not have fittingly passed over the production of the spiritual creature, and therefore when we read, "In the beginning God created heaven and earth," a spiritual nature as yet formless is to be understood by the word "heaven," and formless matter of the corporeal creature by the word "earth." And spiritual nature was formed first, as being of higher dignity than corporeal. The forming, therefore, of this spiritual nature is signified by the production of light, that is to say, of spiritual light. For a spiritual nature receives its form by the enlightenment whereby it is led to adhere to the Word of God.

Other writers think that the production of spiritual creatures was purposely omitted by Moses, and give various reasons. Basil [Hom. i in Hexaem.] says that Moses begins his narrative from the beginning of time which belongs to sensible things; but that the spiritual or angelic creation is passed over, as created beforehand.

Chrysostom [Hom. ii in Genes.] gives as a reason for the omission that Moses was addressing an ignorant people, to whom material things alone appealed, and whom he was endeavoring to withdraw from the service of idols. It would have been to them a pretext for idolatry if he had spoken to them of natures spiritual in substance and nobler than all corporeal creatures; for they would have paid them Divine worship, since they were prone to worship as gods even the sun, moon, and stars, which was forbidden them (Deuteronomy 4).

But mention is made of several kinds of formlessness, in regard to the corporeal creature. One is where we read that "the earth was void and empty," and another where it is said that "darkness was upon the face of the deep." Now it seems to be required, for two reasons, that the formlessness of darkness should be removed first of all by the production of light. In the first place because light is a quality of the first body, as was stated (3), and thus by means of light it was fitting that the world should first receive its form. The second reason is because light is a common quality. For light is common to terrestrial and celestial bodies. But as in knowledge we proceed from general principles, so do we in work of every kind. For the living thing is generated before the animal, and the animal before the man, as is shown in De Gener. Anim. ii, 3. It was fitting, then, as an evidence of the Divine wisdom, that among the works of distinction the production of light should take first place, since light is a form of the primary body, and because it is more common quality.

Basil [Hom. ii in Hexaem.], indeed, adds a third reason: that all other things are made manifest by light. And there is yet a fourth, already touched upon in the objections; that day cannot be unless light exists, which was made therefore on the first day.

[I.q.67.a.4.ad.3] Basil says (Hom. ii in Hexaem.) that day and night were then caused by expansion and contraction of light, rather than by movement. But Augustine objects to this (Gen. ad lit. i), that there was no reason for this vicissitude of expansion and contraction since there were neither men nor animals on the earth at that time, for whose service this was required. Nor does the nature of a luminous body seem to admit of the withdrawal of light, so long as the body is actually present; though this might be effected by a miracle. As to this, however, Augustine remarks (Gen. ad lit. i) that in the first founding of the order of nature we must not look for miracles, but for what is in accordance with nature. We hold, then, that the movement of the heavens is twofold. Of these movements, one is common to the entire heaven, and is the cause of day and night. This, as it seems, had its beginning on the first day. The other varies in proportion as it affects various bodies, and by its variations is the cause of the succession of days, months, and years. Thus it is, that in the account of the first day the distinction between day and night alone is mentioned; this distinction being brought about by the common movement of the heavens. The further distinction into successive days, seasons, and years recorded as begun on the fourth day, in the words, "let them be for seasons, and for days, and years" is due to proper movements.

[I.q.67.a.4.ad.4] As Augustine teaches (Confess. xii; Gen. ad lit. 1,15), formlessness did not precede forms in duration; and so we must understand the production of light to signify the formation of spiritual creatures, not, indeed, with the perfection of glory, in which they were not created, but with the perfection of grace, which they possessed from their creation as said above (Question 62, Article 3). Thus the division of light from darkness will denote the distinction of the spiritual creature from other created things as yet without form. But if all created things received their form at the same time, the darkness must be held to mean the spiritual darkness of the wicked, not as existing from the beginning but such as God foresaw would exist.

The Summa Theologica of St. Thomas AquinasSecond and Revised Edition, 1920Literally translated by Fathers of the English Dominican ProvinceOnline Edition Copyright © 2009 by Kevin Knight Nihil Obstat. F. Innocentius Apap, O.P., S.T.M., Censor. Theol.Imprimatur. Edus. Canonicus Surmont, Vicarius Generalis. Westmonasterii.APPROBATIO ORDINISNihil Obstat. F. Raphael Moss, O.P., S.T.L. and F. Leo Moore, O.P., S.T.L.Imprimatur. F. Beda Jarrett, O.P., S.T.L., A.M., Prior Provincialis AngliæMARIÆ IMMACULATÆ - SEDI SAPIENTIÆ