A man’s got to know his limitations.
1 Hence, since separate substances cannot be known by us in this life in the preceding ways, the question remains whether we may understand these separate substances in any way during this life.
2 Themistius tries to show that it is possible, by an argument from a less important case. Separate substances are indeed more intelligible than material ones; the latter are intelligible, in so far as they are made to be actually understood by the agent intellect, but the former are intelligible in themselves. Therefore, if our intellect comprehends these material substances, it is naturally much more capable of understanding separate substances.
3 Now, this argument must be judged in different ways, depending on the various opinions concerning the possible intellect. For, if the possible intellect is not a power which depends on matter, and again if it is separate in being from body, as Averroes supposes, then it follows that it has no necessary relation to material things. Consequently, things that are more intelligible in themselves will be more intelligible to it. But then it seems to follow that, since we understand from the start by means of the possible intellect, we therefore understand separate substances from the start: which is clearly false.
4 But Averroes tried to avoid this difficulty by the explanation which has been mentioned above, in connection with his opinion. And this is plainly false, on the basis of what we have established.
5 However, if the possible intellect is not separated in being from body, then by virtue of such a union in being with body it has a necessary relation to material things, so that it could not reach a knowledge of other things except by means of these material things.
Hence, it does not follow that, if separate substances are more intelligible in themselves, they are for this reason more intelligible to our intellect. And the words of Aristotle in Metaphysics II [1: 993b 9] prove this. For he says there that “the difficulty of understanding these things comes from us not from them, for our intellect is to the most evident things, as the eye of the owl is to the light of the sun.” Hence, since separate substances cannot be understood through material things that are understood, as was shown above, it follows that our possible intellect can in no way understand separate substances.
Notes The first paragraph of 5 is, of course, the most important. As is the first part of 6.
6 This is also evident from the relation of the possible intellect to the agent intellect. A passive potency is only a potency in regard to those things that are within the power of its proper active principle; for, to every passive potency in nature there corresponds an active potency; otherwise, the passive potency would be useless, for it could not be reduced to act except through an active potency.
Hence we see that the visual power is only receptive of colors which are illuminated by light.
Now, the possible intellect, since it is a passive power in some sense, has its proper corresponding agent, namely, the agent intellect which is related to the possible intellect as light is to sight.
So, the possible intellect is only in potency to those intelligible objects which are made by the agent intellect. Hence, Aristotle, describing both intellects in Book III of On the Soul [5: 430a 14], says that the possible intellect is “the capacity to become all things,” while the agent intellect is “the capacity to make all things”; so, each potency is understood to be referred to the same thing, but one is active and the other passive, Thus, since separate substances are not made to be actually intelligible by the agent intellect, but only material substances are, the possible intellect only includes the latter within its scope. Therefore, we cannot understand separate substances through it.
7 For this point Aristotle made use of an appropriate example, for the eye of an owl can never see the light of the sun; though Averroes tries to ruin this example by saying that the similarity between our intellect in relation to separate substances and the eye of the owl in relation to the light of the sun does not extend to impossibility, but only to difficulty. He gives a proof for this, in the same place, using the following argument: If those things which are understood in themselves, namely, separate substances, were not possible for us to understand, they would be for no purpose, just as if there were a visible object which could not be seen by any visual power.
Notes Obviously, the state of an owl’s site is only incidental to this.
8 How frivolous this argument is, is quite apparent. For, though these substances might never be understood by us, they are nonetheless understood by themselves. Hence, they are not intelligible in a purposeless way, as the sun (to pursue Aristotle’s example) is visible, yet not in a purposeless way, simply because the owl cannot see it. For man and other animals can see it.
9 And thus, the possible intellect, if it be granted that it is united with the body in being, cannot understand separate substances. However, it makes a difference how one thinks about its substance. For, if it is supposed to be a material power, capable of generation and corruption, as some have claimed, then it follows that it is limited by its own substance to the understanding of material things. Consequently, that it could in no way understand separate substances is quite necessary, since it could not be separate in its own being.
On the other hand, if the possible intellect, though united with a body, is, however, incorruptible and not dependent on matter in its actual being, as we showed above, it follows that the limitation to the understanding of material things accrues to it as a result of its union with the body. Consequently, when the soul will have been separated from this body, the possible intellect will be able to understand things that are intelligible in themselves, through the light of the agent intellect, which is the likeness in the intellectual soul of the light which is present in separate substances.
10 And this is the view of our faith, concerning the understanding of separate substances by us after death, and not in this life.