See the first post in this series for an explanation and guide of our tour of
This may be proved in three ways. The first…
Summa Contra Gentiles. All posts are under the category SAMT
Nobody alive appears to believe that all men share one soul. If pantheism is defined as God is the universe, than that all share one soul must be mantheism (sorry). This Chapter continues 41 original arguments, but I’m paring them back here since this is no longer a live controversy.
Chapter 73 That there is no one possible intellect in all men (alternate translation) We’re still using the alternate translation this week.
1 On the basis of what has already been said it can be clearly demonstrated that there is not one possible intellect of all present, future and past men, as Averroes imagined.
Notes For those who don’t know, Averroes was a Muslim theologian-philosopher of the 12th century.
2 For it has been proved that the substance of the intellect is united to the human body as its form. But one form cannot possibly exist in more than one matter, because the proper act comes to be in the proper potentiality, since they are proportioned to one another. Therefore, there is not one intellect of all men…
Notes This argument is conclusive enough, but there are still some twists and turns of interest.
4 Again, Aristotle in De anima I  takes the ancients to task for discussing the soul without saying anything about its proper recipient, “as if it were possible, as in the Pythagorean fables, that any soul might put on any body.” It is, then, impossible for the soul of a dog to enter the body of a wolf, or for a man’s soul to enter any body other than a man’s. But the proportion between man’s soul and man’s body is the same as between this man’s soul and this man’s body. Therefore, the soul of this man cannot possibly enter a body other than his own. But it is this man’s soul by which this man understands: man understands by his soul, as Aristotle puts it in De anima I . Hence, this man and that man have not the same intellect.
Notes Well, and so much for all those identity-swapping tales and movies, which used to swap old and young, and now swap male and female. Curious.
5 Then, too, a thing owes its being and its unity to the same principle, for unity and being are consequent upon one another. But every thing has being through its form. Therefore, a thing’s unity follows upon the unity of its form. Hence, there cannot possibly be one form of diverse individual things. But the form of this particular man is his intellective soul. Therefore, it is impossible that there should be one intellect for all men…
7 Now, the Commentator Averroes replies to these arguments by saying that the possible intellect comes into contact with us through its form, that is, by the intelligible species, whose single subject is the phantasm existing in us and which is distinct in distinct subjects. Thus, the possible intellect is particularized in diverse subjects, not by reason of its substance but of its form.
8 It is clear from what has been said above that this reply is worthless. For, if the possible intellect makes contact with us only in that way, man’s understanding is rendered impossible, as we have shown…
Notes Worthless? That St Thomas is so judgmental, isn’t he?
10 Moreover, a thing derives its species, not from that which is in potentiality, but from that which is in act. Yet the phantasm, as particularized, has only a potentially intelligible being. Therefore, it is not to the phantasm as particularized that this individual owes the specific character of intellective animal, which is the nature of man. And so we have the same result as before, namely, that the thing from which man’s specific nature is derived is not particularized in diverse subjects…
Notes The difference between potency and act is ever with us!
13 The source of man’s specific nature must always remain the same in the same individual as long as the individual continues to be; otherwise, the individual would not always be of one and the same species, but sometimes of this one and sometimes of that one. But phantasms do not always remain the same in one man; rather, some new ones appear, while some old ones pass away. Therefore, the human individual neither acquires his specific nature through the phantasm nor by its means is he brought into contact with the principle of his specific essence, namely, the possible intellect.
14 Now, if it be argued that this man does not derive his specific nature from the phantasms themselves but from the powers in which the phantasms reside, namely, imagination, memory, and cogitation—the latter, which Aristotle in De anima calls the passive intellect, being proper to man—even so the same impossibilities ensue. For, since the cogitative power is operationally limited to particular things, makes its judgments on the basis of particular intentions, and acts by means of a bodily organ, it is not above the generic level of the sensitive soul. Now, man is not a man in virtue of his sensitive soul, but an animal. Therefore, it still remains that the only thing particularized in us is that which belongs to man as an animal.
15 Moreover, the cogitative power, since it operates by means of an organ, is not that whereby we understand, for understanding is not the operation of an organ. Now, that whereby we understand is that by which man is man, since understanding is man’s proper operation, flowing from his specific nature. Consequently, it is not by the cogitative power that this individual is a man, nor is it by this power that man differs substantially from the brutes, as the Commentator imagines…
Notes Understanding is not the operation of an organ: we are not our brains! Animals don’t understand: man does.
24 It is with respect to the conclusions of demonstrations, moreover, that there is science. For a demonstration is “a syllogism productive of scientific knowledge,” as Aristotle says in Posterior Analytics I . Now, the conclusions of demonstrations are universals, and so, too, are their principles. Therefore, science will reside in that power which is cognizant of universals. But the passive intellect has no knowledge of universals, but only of particular intentions. Hence, it is not the subject of the habit of science…
29 And if there is one possible intellect for all men, it must be granted that if (as the Averroists assert) men have always existed, then the possible intellect has always existed, and much more the agent intellect, because “the agent is superior to the patient,” as Aristotle says. Now, if both the agent and the recipient are eternal, the things received must be eternal. It would then follow that the intelligible species existed from all eternity in the possible intellect; so, in that case, the latter receives no intelligible species anew. But it is only as the subjects from which intelligible species may be derived that sense and imagination have any necessary role to play in the understanding of things. Therefore, neither sense nor imagination will be necessary for understanding. And thus we shall come back to Plato’s theory that we do not acquire knowledge through the senses, but are awakened by them to the remembrance of things we knew before…
Notes Worse, if we’re all sharing the same learned things, we’re going to have an impossible time explaining our stupidity. The Averroist argument doesn’t explain how, if all understand as one, individuals are ignorant. As these next paragraphs show.
34 Since the intellect is a higher power than the sense, its unity must be greater. This explains the observed fact of one intellect exercising judgment upon diverse kinds of sensible things belonging to diverse sensitive powers. And from this we can gather that the operations belonging to the various sensitive powers are united in the one intellect. Now, some of the sensitive powers only receive—the senses, for instance; while some retain, as imagination and memory, which therefore are called store-houses. The possible intellect, then, must both receive and retain what it has received…
39 Then, too, the possible intellect, according to Aristotle, is that “whereby the soul and man understand.” But, if the possible intellect is one in all men and is eternal, then all the intelligible species of the things that are or have been known by any men whatever must already be received in it. Therefore, each of us, since we understand by the possible intellect, and, in fact, our act of understanding is itself the possible intellect’s act of understanding, will understand all that is or has been understood by anyone whatever; which is plainly false…
41 But, that this reply cannot wholly avoid the difficulty is made clear as follows. When the possible intellect has been actualized by the reception of the intelligible species, it can act of itself, as Aristotle says in De anima III .
This accounts for the experienced fact that when we have once acquired knowledge of a thing, it is in our power to consider it again at will. And since we are able to form phantasms adapted to the thinking that we wish to do, they are no hindrance to us [in our reconsideration of things], unless, perhaps, there be an obstacle on the part of the organ to which the phantasm belongs, as in madmen and those afflicted with lethargy, who cannot freely exercise their imagination and memory.
For this reason Aristotle says in Physics VIII that one already possessed of the habit of science, though he be considering potentially, needs no mover to bring him from potentiality to act, except a remover of obstacles, but is himself able to exercise his knowledge at will.
If, however, the intelligible species of all sciences are present in the possible intellect—which the hypothesis of its unicity and eternity necessarily implies—then that intellect will require phantasms, just as one already in possession of a science needs them in order to think in terms of that science; this the intellect cannot do without phantasms.
Therefore, since every man understands by the possible intellect as a result of its being actualized by the intelligible species, every man will be able to apply his mind at will to the things known in every science. This is manifestly false, since in that case no one would need a teacher in order to acquire a science. Therefore, the possible intellect is not one and eternal.
1 And sometimes even having a teacher is no guarantee of acquiring a science (sorry). Let us have madmen and lethargy (a burgeoning science lurks) as the final word!