Chapter 45 — That it is impossible in this life to understand separate substances

Since, then, in this life separate substances cannot be known by us in the ways mentioned above, (Cc. 41–44.) it remains for us to inquire whether we be able to understand separate substances in this life in any way at all.

Themistius (A.D. 317–387. Paraphr. On the Soul ch. 3, [51].) seeks to prove that this is possible by an argument a fortiori. For separate substances are more intelligible than material things, since the latter are intelligible insofar as the active intellect causes them to be actually understood, whereas the former are intelligible in themselves. If, therefore, our intellect understands these material things, much more is it adapted to understand separate substances.

This argument must be appraised in the light of the various opinions about the possible intellect. For if the possible intellect is a power independent of matter, and has its being apart from the body, as Averroes maintains, it will follow that it has no necessary relation to things material; so that the more a thing is intelligible in itself, the more will it be intelligible to the possible intellect. But then it would seem to follow, since we understand from the beginning by means of the possible intellect, that we understand separate substances from the beginning: which is clearly false.

Averroes seeks to avoid this difficulty, as we have explained above in setting forth his opinion, which we proved to be false.

If, however, the possible intellect is not separate from the body in its very being, it has a necessary relation to material things from the very fact that it is united in being to such a body, so that only through them can it acquire knowledge of other things. Hence it does not follow that separate substances are more intelligible to our intellect if they are more intelligible in themselves. This is proved by the words of Aristotle. For he says there that the difficulty of understanding those things is in us and not in them because our intellect stands in relation to things most evident as the eye of the owl to the sunlight. (Metaphysics 2.9.) Consequently, seeing that we cannot arrive at understanding separate substances through understanding material things, as we have proved, (Ch. 41.) it follows that our possible intellect can in no way understand separate substances.

This appears again from the relation of the possible to the active intellect. For a passive power is in potency to those things only which are included in the range of its proper active principle, for every passive power has a corresponding active power in nature: otherwise passive power would be useless, since it cannot be brought to act except by an active principle. Hence we find that the sight is not receptive of anything other than colors which are enlightened by the light. Now the possible intellect is a power in a certain sense passive, and therefore it has its corresponding agent, namely the active intellect, which stands in relation to the possible intellect as light to the sight. Consequently, the possible intellect is in potency to those intelligible objects only which have been made so by the active intellect. Therefore, Aristotle, in describing each intellect, says that the possible intellect is the power to become all things, while the active intellect is the medium of making all things: (On the Soul 3.5.) so that the power in either case refers to the same objects, being active in the one and passive in the other. Since, then, separate substances are not made actually intelligible by the active intellect, and only material things are so made, it follows that the possible intellect extends to these alone. Therefore, we cannot understand separate substances thereby.

Therefore, Aristotle employed a fitting example: for the owl’s eye can never see the light of the sun. And yet Averroes tries to depreciate this example, saying that the likeness between our intellect in relation to separate substances and the owl’s eye in relation to the sun’s light is one of difficulty, not of impossibility: and he proves this as follows. If it were impossible for us to understand things intelligible in themselves (namely, separate substances), they would be intelligible without purpose, as a thing would be visible to no purpose if it could not be seen by any sight.

Now this argument is clearly of no account at all. For, even if these substances be never understood by us, they are understood by themselves, so that they would not be intelligible without purpose, as—to continue Aristotle’s comparison—neither is the sun uselessly visible because the owl cannot see it, since man and other animals can see it.

Accordingly, if we suppose the possible intellect to be united in being to the body, it cannot understand separate substances. It makes a difference, however, what we hold with regard to its substance. For if we suppose it to be a material force subject to generation and corruption, as some have maintained, (Cf. ch. 42.) it would follow that by its very substance it is confined to the understanding of material things: consequently, it would in no way be able to understand separate substances, since it could not possibly itself be separate.

On the other hand, if the possible intellect, although united to the body, be incorruptible and independent of matter in its being (as we have proved above), (Bk. 2, ch. 79.) it follows that its being confined to the understanding of material things is incidental to it through its union with the body. And so, when the soul will have been separated from the body, the possible intellect will be able to understand things that are intelligible in themselves (namely, separate substances) by the light of the active intellect, which in the soul is like the intellectual light that is in separate substances.

This is what our faith holds about our understanding separate substances after death and not in this life.