This chapter, and the next, exist to squash a couple of subtle, technical errors. They require close reading to grasp. It’s best to at least skim: don’t skip. Reminder: An intellectual substance is an angel.
1 Because Alexander [of Aphrodisias] claimed that the possible intellect is capable of being generated and corrupted, in the sense that it is “a perfection of human nature resulting from a mixture of the elements,” as we saw in Book Two, and since it is not possible for such a power to transcend material conditions, he maintained that our possible intellect can never reach an understanding of separate substances. Yet he asserted that, in our present state of life, we are able to understand separate substances.
2 In fact, he tried to show this in the following way. Whenever anything has reached maturity in its process of generation and has come to the full perfection of its substance, the operation proper to it will be at its peak, whether as action or as passion. For, as operation is consequent upon substance, so also is the perfection of operation a result of the perfection of substance. Hence, an animal, when it has become wholly perfect, is able to walk by itself.
Now, the habitual understanding which is simply “intelligible species made to exist in the possible intellect by the agent intellect” has a twofold operation: one, to make potentially understood things to be actually understood, and it owes this to the role of the agent intellect; and the second is actually to understand the objects of understanding.
These two things, then, man can do through an intellectual habit. So, whenever the generating of the habitual understanding has reached completion, both of these stated operations will be at their peak in it. Now, it always approaches the peak perfection of its generation when it acquires new kinds of objects of understanding. And thus, its process of generation must be completed at some time, unless there be an impediment, because no process of generation tends to an indefinite termination. So, it will reach completion whenever both operations are habitually present in the intellect, by virtue of the fact that it makes all the potential objects of understanding actual, which is the completion of the first operation, and because of the fact that it understands all intelligible objects, both separate and not separate.
3 Now, since according to his opinion the possible intellect cannot understand separate substances, as has already been said, he thought that we will understand separate substances through the habitual understanding, in so far as the agent intellect, which he supposes to be a separate substance, becomes the form of the habitual understanding, and a form for us ourselves. Thus, we will understand through it, as we now understand through the possible intellect; and since it is the function of the power of the agent intellect to make all things which are potentially intelligible to be actually understood, and to understand the separate substances, we will understand separate substances in this life, and also all non-separate intelligible things.
4 So, according to this theory, we reach the knowledge of separate substances through this knowledge which comes from the phantasms, not in the sense that these phantasms and the things understood through them are means for the knowing of separate substances (as is the case with the speculative sciences, according to the position advanced in the preceding chapter), but, rather, in so far as the intelligible species are certain dispositions within us to the kind of form that the agent intellect is. And this is the first point on which these two opinions differ.
5 Hence, when the habitual understanding will be perfected through the production in us by the agent intellect of these intelligible species, the agent intellect will itself become a form for us, as we have said. And he calls this the “acquired understanding,” which, according to their statement, Aristotle says comes from outside. And so, though the ultimate human perfection is not in the speculative sciences, as the preceding opinion claimed, man is disposed through these sciences to the attainment of the ultimate perfection. And this is the second point on which the first and second opinions differ.
6 However, they differ on a third point, because, according to the first opinion, our actual understanding of the agent intellect is the cause of its being united with us. Whereas, according to the second opinion, the converse is the case, for, since it is united with us as a form, we understand it and the other separate substances.
7 Now, these statements are unreasonable. Indeed, the habitual understanding, as also the possible understanding, is supposed by Alexander to be generable and corruptible. Now, the eternal cannot become the form of the generable and corruptible, according to him. For this reason, he claims that the possible intellect, which is united to us as a form, is generable and corruptible, while the agent intellect which is incorruptible is a separate substance. Hence, since the agent intellect, according to Alexander, is supposed to be an eternal separate substance, it will be impossible for the agent intellect to become the form of the habitual intellect.
8 Moreover, the form of the intellect, as intellect, is the intelligible object, just as the form of the sense is the sensible object; indeed, the intellect receives nothing, strictly speaking, except in an intellectual way, just as the sense power only receives sensitively. So, if the agent intellect cannot be an intelligible object through the habitual intellect, then it will be impossible for it to be its form.
9 Besides, we are said to understand something in three ways. First, as we understand by means of the intellect which is the power from which such an operation proceeds; hence, both the intellect itself is said to understand, and also the intellect’s act of understanding becomes our act of understanding. Second, we understand by means of an intelligible species; of course, we are not said to understand by it, in the sense that it understands, but because the intellective power is actually perfected by it, as the visual power is by the species of color. Third, we understand as by an intermediary through the knowing of which we come to the knowledge of something else.
10 So, if at some point man understands separate substances through the agent intellect, this must be explained by one of these ways that have been mentioned. Now, it is not explained by the third way, for Alexander did not admit that either the possible or the habitual intellect understands the agent intellect. Nor, indeed, is it in the second way, for to understand through an intelligible species is the attribute of the intellective power for which this intelligible species is the form.
Now, Alexander did not grant that the possible intellect or the habitual intellect understands separate substances; hence, it is not possible for us to understand separate substances through the agent intellect in the same way that we understand other things through an intelligible species. But, if it is as through an intellective power, then the agent intellect’s act of understanding must be man’s act of understanding. Now, this cannot be so unless one actual being is made from the substance of the agent intellect and the substance of man; indeed, it is impossible if they are two substances with different acts of being, for the operation of the one to be the operation of the other.
Therefore, the agent intellect will be one existing being with man, not one accidentally, for then the agent intellect would be not a substance but an accident, as is the case when a thing that is one being accidentally is made from color and a body. The conclusion remains, then, that the agent intellect is united with man in substantial being. It will be, then, either the human soul or a part of it, and not some separate substance as Alexander claimed. Therefore, it cannot be maintained, on the basis of Alexander’s opinion, that man understands separate substances.
11 Furthermore, if the agent intellect at any time becomes the form of one man, so that he is enabled to understand through it, by the same token it could become the form of another man similarly understanding through it. It will know, then, that two men will understand at the same time through the agent intellect as through their own form. This is so because the agent intellect’s own act of understanding is the act of understanding of the man who understands through it, as was said already. Therefore, there will be the same act of understanding for two intelligent beings; and this is impossible.
12 As a matter of fact, his theory is entirely frivolous. First of all because, whenever the process of generation is perfected in any member of a genus its operation must be perfected, but, of course, according to the manner of its own genus and not according to the mode of a higher genus. For instance, when the generation of air is perfected it has a development and complete movement upward, but not such that it is moved to the place proper to fire. Similarly, when the development of the habitual intellect is completed its operation of understanding will be completed according to its own mode, but not according to the mode whereby separate substances understand, so that it may understand separate substances. Hence, from the generation of the habitual intellect one cannot conclude that man will understand separate substance at some time.
13 Secondly, it is frivolous because the perfection of an operation belongs to the same power to which the operation itself belongs. So, if to understand separate substances be a perfection of the operation of the habitual intellect, it follows that the habitual intellect understands separate substances at some point in time. Now, Alexander does not claim this, for it would follow that to understand separate substances would depend on the speculative sciences which are included under the notion of habitual understanding.
14 Thirdly, it is frivolous because the generation of things that begin to be generated is nearly always brought to completion, since all processes of generating things are due to determinate causes which achieve their effects, either always, or in the majority of cases. If, then, the perfection of action also follows upon the completion of generation, it must also be the case that perfect operation accompanies the generated things, either always, or in the majority of cases. Now, the actual understanding of separate substances is not achieved by those who apply themselves to the development of habitual understanding, either in most cases or always; on the contrary, no man has openly declared that be had achieved this perfection. Therefore, the perfection of the operation of habitual understanding does not consist in the actual understanding of separate substances.