Dist. 13, Art. 3, Q. 1
by St. Bonaventure
Source text: Public Domain Mark 1.0. English translation/apparatus/encoding: CC BY-NC 4.0, Wroot Press.
https://bonaventure.wrootpress.com/browse/2/d/13/q/bon-sent-II-d13-a3-q1
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## ARTICLE III.

### *On the effect and irradiation of light.*

Next it is asked about the effect and irradiation of light. And concerning this two [things] are asked. First it is asked, whether the *lumen* which is emitted from a luminous body is a body, or a corporeal quality. Secondly, given that it is a quality, [there is the] question whether it is substantial or accidental.

### Question I. *Whether lumen, which goes forth from a luminous body, is a body.*

Concerning the first it is so proceeded and shown first, that the *lumen* which goes forth from a luminous body is a body.

*Against the opposite.*

1. Everything which is moved through itself locally and dimensionally is a body; but the ray or *lumen* going out from the sun is moved locally — that is, from east to west: therefore both the ray and the *lumen* is a body.

2. Likewise, nothing is reverberated and driven back from a body except a body — «*for it is impossible that a non-body be moved by a body*»; but reverberation of light and rays occurs at an opaque body: therefore both *lumen* and ray is a body.

3. Likewise, it is impossible that there be refraction and intersection except of bodies; but from the reverberation of light at a concave mirror occurs an intersection and refraction of rays: therefore it seems that both *lumen* and ray is a body.

4. Likewise, everything which has the three dimensions is a body; but *lumen* in a medium has the three dimensions, because it is diffused according to every position, nor is it only on the surface — rather it even penetrates the air into the depth: therefore it seems that *lumen* in a medium is a body.

5. Likewise, suppose that the sun existed and around it there were a vacuum: since the sun is able by the power of light, without extrinsic help — unless it has [something] resisting — to diffuse its *lumen*; and in that vacuum it would have no resistance; in the same place it would diffuse its *lumen*; but that *lumen* would not be in another sustaining body: therefore it seems that it would be a substance existing through itself; and not spiritual — this is established: therefore corporeal.

6. Likewise, that which can generate a body is a body; but *lumen* diffused in a medium can generate a body — namely fire — by its multiplication: therefore *lumen* in a medium is a body.

*On the contrary:*

*Foundations.*

1. The Philosopher in the second of *On the Soul*: «*Lumen is neither a body nor an effluxion of a body*».

2. Likewise, this is seen by reason through its opposite. For darkness is opposed to *lumen* privatively: if therefore privation is not of body but of form, *lumen* is not a body but a form.

3. Likewise, this is seen by *motion*. For no body is moved suddenly according to place; but light alters suddenly, because in an instant it comes from east to west: therefore *lumen* is not a body. If you say that it is not moved suddenly but quickly [*repente*]; this cannot stand according to the Philosopher, because if it were moved quickly — that is, imperceptibly in some space — in a larger space the succession could be sensed, as is clear in sound: therefore etc.

4. Likewise, no body is moved more swiftly than the body of the first movable, because that motion is the most perfect of all motions and therefore the swiftest; but *lumen* from east to west is moved much more swiftly than the first orb is moved, because light [moves] in an instant, and that [orb] at least in twelve hours: therefore *lumen* is not a body.

5. Likewise, no body is moved simultaneously and at once toward opposite parts; but *lumen* is simultaneously and at once moved toward opposite parts, because it is diffused upward and downward, before and behind, on the right and on the left: therefore it cannot be a body.

6. Likewise, it is impossible that two unmixed bodies which do not augment one another be simultaneously [in the same place]; but *lumen* is unmixed with the air, and does not augment the air itself, and yet is simultaneous [with it]: therefore it is not a body. That it is impossible for two bodies to be at once [in the same place], the Philosopher says, and for this there are reasons which can be omitted at present, since they are brought forward in the fourth [book], where the penetrability of the glorified body is treated.

7. Likewise, no body has its being in *continual coming-to-be*; but *lumen* in the air has its being in coming-to-be, because it continually goes forth from the sun, as Augustine says: therefore it is impossible that it be a body.

8. Likewise, if *lumen* is a body, either it is from something or it is from nothing. If from nothing, then it is by creation — therefore *lumen* is from God alone, since to create belongs to Him alone. If from something, I ask, from what? either from the body by which it is caused, or from the body in which it is received. It is established that not from the body in which it is received, because *lumen* is not produced out of the air — for then it could remain there when the sun withdraws. If from the body by which it is caused, then it seems that the luminous body, in the emission of *lumen*, loses something of its substance and matter, and thus it seems that by now the sun ought to be consumed.

### CONCLUSION.

> *Lumen and ray, as properly taken, is not a body.*

**I respond:** For the understanding of what has been said, it must be noted that on this matter there have been four opinions.

*Opinion 1.* For some have wished to say that both *lumen* and ray in the medium is a *body*, and the going-out of the rays themselves from the sun is like the going-out of streams from a fountain. For just as from a fountain streams proceed, which are bodies and of the same nature as the fountain, so they say it is in the rays and the sun. And if you object to them that it seems that the substance of the sun and of other luminaries would by now be nearly consumed, they answer that, just as the substance of a fountain is not consumed — because as emission occurs, so also restoration occurs — so they say that the substance of the sun is not consumed, because just as outwardly downward it emits its *lumen*, so by the power of its rays it draws upward vapors to itself, by which it is restored, as a body by food — to such a degree that it neither fails nor decreases. And this Seneca seems to have held. — *It is disproven.* This position, however, is against philosophy, which says that celestial bodies are entirely incorruptible.

*Opinion 2.* The second position, however, is that *lumen* is a *body*, and similarly the rays — and the procession of the rays themselves from the sun is like that of branches from a root, especially if it were so that the root could immediately produce a tree out of itself, assisted by divine power, as perhaps was the case in the first condition of things; and just as the root would not be diminished if it so produced a tree, and yet the branches would always be said to issue from that root — not because they go forth anew, but because they are continuous with their origin — so they say it is also in the sun's rays. For when God made the sun as the origin and principle of *lumen*, simultaneously with this He gave to it the ramification of rays; and the sun is continually said to emit those rays because those rays are never separated from their origin; but just as the sun is moved, so the rays are carried around — they are not generated anew; for the same rays which it emitted from the beginning upon the earth, it emits even now. — *It is disproven.* But suppose that the sun were darkened, as in the passion of Christ is believed to have happened; then it seems that it would have been necessary from then on for the rays to be renewed, and thus to be created anew, if they were bodies.

*Opinion 3.* The third position is that both *lumen* and ray in the medium is a *body*; and its production as regards *form* is from the sun, but as regards *matter* is from the Creator. For they say that this pertains to the perfection of the universe — that, just as there is some creature which as regards matter and form is immediately from God, like an angel; and some which as regards form is immediately from God and as regards matter is from nature, like man; so also there is a third genus, which as regards form is from a creature and as regards matter is from God. — *It is disproven.* But this does not seem probable, since God never creates matter apart from some form.

Although, however, each of these three positions specifically says something improbable concerning the origin of *lumen* from light, nevertheless all of them are commonly disproven by this — that they say *lumen* in the medium to be a body — both on account of its diffusion, which is sudden; and also on account of its coexistence with the air, which is unmixed; and also on account of its production, which is neither from matter nor ever separated from its [source's] existence; rather, just as it continually is, so it is continually generated; as Augustine says that *lumen* has its permanence through the continual influence of the sun.

*Opinion 4 and conclusion.* And therefore there is a fourth position, in concord with reason and philosophy: that *lumen* and ray, if it names precisely that which has its rise from light, is neither a body nor an effluxion of a body, as the reasons adduced for this show. But if *ray* be called air illuminated according to *diameter*, and *lumen* air illuminated according to *depth*, then in this way ray and *lumen* can be called a body. — *Conclusion 2.* But as *lumen* and ray are properly taken in the medium, they are not a body.

*Solution of the opposing [arguments].*

1. To that which is first objected, that it is moved locally: it must be said that just as we see in a species generated from color that it is moved in two ways — and one motion is by diffusion, proceeding from the object body to the mirror, but the other motion [is] according as it seems to be moved in the mirror at the motion of the object body — and the first is not local motion, but [motion] of *generation*; but by the second motion it is not moved through itself, but per accidens — *Distinction.* so it must be understood in the matter at hand, that the motion of *lumen* which is by its going forth from the shining body is not properly local change, but rather the *generation* and *diffusion* of *lumen*; and this is clear from this — that it occurs suddenly in however great a space. — *Note.* The other motion, however, which is by the carrying of the rays themselves over the earth together with the sun itself — this is only per accidens, just as a power itself is moved at the motion of its influencing principle; and yet the power is not a body. So it must be understood of *lumen*, that it is related to the luminous body in the manner of an *influxed power*. Hence the Damascene: «*We say, on account of the lumen that proceeds from it, that fire shines; and we do not posit the lumen which is from it to be the ministerial organ of the fire, but rather a more natural power*».

2. To that which is objected, that the rays are reverberated from a body: it must be said that the reverberation of something from something can be in two ways. — *Twofold reverberation.* One, from the collision of two [bodies] meeting one another, as a ball is reverberated from a wall; another, from the ineptitude of the patient to receive the power of the agent — and thus a ray is reverberated from an opaque body. For the sun, or any other luminous body, has the power

of diffusing *lumen* up to some determinate space, since it is of finite power; and as long as that power extends itself, *lumen* is multiplied, if there be a suitable receiver; — *Concerning perspective.* but when, before the termination of that power, some body meets [the ray] which is not suitable for its reception, by this very fact that *lumen* could not multiply itself further forward, it multiplies itself backward — not from the power of the resisting body, but from the power of the first mover. Hence, when reverberation of a ray occurs in water, with the water moved, the ray is moved — not because the water is the moving principle, but [because] the first power producing the ray, which, with occasion received from the water, could reflect the ray, and with occasion received from the same, can vary the reflection and thus move the ray. — As to what is said: *it is impossible for a non-body to be repelled by a body*; — *Distinction.* it must be said that if there is something so non-body that it be a spirit, this is true. But if it is so non-body that it nevertheless needs a body to carry it, then it can without doubt be repelled — as has been said in the case of *lumen*, and as is manifest in the image which shines back in a mirror because of the application of lead with glass, which is an opaque body. For if there were only the glass by itself, which is a pervious body, the species would pass through and would not return to the eye, as is clear by sensible experiment.

3. To that which is objected, that there occurs intersection and refraction of rays: it must be said that this is said by reason of the conjoined air, which by the power of the rays concurring there is subtilized and moved; and by reason of this the rays are also said to be refracted, when from the multiplication along opposite ways, by progression and regression, there occurs a certain multiplication and aggregation of light, and a subtilization of the air around a polished body — from which it happens that the heat-effect of the ray is intensified, and fire is generated in the same place through the intensification of heat from the air so subtilized.

4. To that which is objected, that *lumen* has the three dimensions in the medium: — *Distinction.* it must be said that something can have dimension in two ways: either from *itself*, or by reason *of that in which it is*. If from itself, then it is a body; if from elsewhere, it is not necessary. For so whiteness in white lead and snow has the three dimensions — [things] which are white inside and outside.

5. To that which is objected, that if there were a vacuum around the sun, that it would illumine; — *On the vacuum and illumination.* it must be said that, although some have said this, it nevertheless does not seem true or probable. For the Philosopher holds the contrary in the second of *On the Soul*, when he says that «*one does not see through a vacuum*»; and Augustine likewise in the twelfth book of the *Confessions*, in the beginning, says thus: «*Where would light be, if it were [there], unless it were present, surpassing in shining and illumining?*» — And there is also a reason against this — that, since *lumen* is a corporeal form, it needs a medium to carry it. And if you ask, what would impede [it]: I say that this is not on account of the presence of an impediment, but on account of the absence of help — just as if someone having great hunger and lacking food cannot eat, not because he is impeded, but because he is not helped.

6. To that which is objected, that *lumen* generates a body: — *Note.* it must be said that *lumen* does not act by its own power, but by the power of the luminous body; but the luminous body does not bring forth a body as regards matter, but only as regards form — and on this account, since *lumen* is that through which it acts, it is not necessary that *lumen* be a body, but it suffices that it be a corporeal form.