SCG 2.75

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WE must now show the inefficacy of such arguments as are adduced to prove the unity of the possible intellect.[1]

For seemingly every form that is one specifically and many in number is individualized by matter: since things that are one in species and many in number, agree in form and differ in matter. Wherefore if the possible intellect is multiplied numerically in different men, whereas it is one in species, it must needs be individualized in this and that man by matter. This is not however by matter which is a part of the intellect itself, because then its reception would be of the same kind as that of primary matter, and it would receive individual forms; which is contrary to the nature of the intellect. It follows, therefore, that it is individualized by matter which is the human body of which it is supposed to be the form. Now every form that is individualized by matter whereof it is the act, is a material form. Because the being of a thing must needs depend on that from which it has its individuality: for just as common principles belong to the essence of the species, so individualizing principles belong to the essence of this particular individual. Hence it follows that the possible intellect is a material form: and consequently that it neither receives anything nor operates without a corporeal organ. And this again is contrary to the nature of the possible intellect. Therefore the possible intellect is not multiplied in different men, but is one for all.

Again. If there were a different possible intellect in this and that man, it would follow that the species understood is numerically distinct in this and that man, though one specifically: for, since the possible intellect is the proper subject of species actually understood, if there be many possible intellects, the intelligible species must needs be multiplied numerically in different intellects. Now species or forms that are the same specifically and different numerically, are individual forms. But these cannot be intelligible, since intelligibles are universal, not particular. Therefore it is impossible for the possible intellect to be multiplied in different human individuals: and consequently it must be one in all.

Again. The master imparts the knowledge that he possesses to his disciple. Either, then, he imparts the same knowledge numerically, or he imparts a knowledge that is different numerically but not specifically. The latter is apparently impossible, since then the master would cause his knowledge to be in his disciple, as he causes his form to be in another by begetting one like to him in species; and this would seem to apply to material agents. It follows, therefore, that he causes the same knowledge numerically to be in his disciple. But this would be impossible unless there were one possible intellect for both. Therefore seemingly there must needs be but one possible intellect for all men.

Nevertheless, just as the aforesaid position is void of truth, as we have proved,[2] so the arguments adduced in support thereof are easy of solution.

For we contend that while the possible intellect is specifically one in different men, it is nevertheless many numerically: yet so as not to lay stress on the fact that the parts of a man do not by themselves belong to the genus or species, but only as principles of the whole. Nor does it follow that it is a material form dependent, as to its being, on the body. For just as it is competent to the human soul in respect of its species to be united to a body of a particular species, so this particular soul differs only numerically from that one through having a habitude to a numerically different body. Thus human souls are individualized,--and consequently the possible intellect also which is a power of the soul,--in relation to the bodies, and not as though their individuality were caused by their bodies.

His second argument fails through not distinguishing between that whereby one understands, and that which is understood. For the species received into the intellect is not that which is understood. Because, since all arts and sciences are about things understood, it would follow that all sciences are about species existing in the possible intellect. And this is clearly false, for no science takes any consideration of such things except Logic and Metaphysics. Nevertheless whatever there is in all the sciences is known through them. Consequently in the process of understanding the species received into the possible intellect is as the thing by which one understands, and not as that which is understood: even as the coloured image in the eye is not that which is seen, but that by which we see. On the other hand that which is understood is the very essence of the things existing outside the soul, even as things outside the soul are seen by corporeal sight: since arts and sciences were devised for the purpose of knowing things as existing in their respective natures.

Nor does it follow that, because science is about universals, universals are subsistent of themselves outside the soul, as Plato maintained. For, although true knowledge requires that knowledge correspond to things, it is not necessary that knowledge and thing should have the same mode of being. Because things that are united in reality are sometimes known separately: thus a thing is at once white and sweet, yet sight knows only the whiteness, and taste only the sweetness. So too the intellect understands a line existing in sensible matter, apart from the sensible matter, although it can also understand it with sensible matter. Now this difference occurs according to the difference of intelligible species received into the intellect: for the species is sometimes an image of quantity alone, and sometimes is an image of a quantitative sensible substance. In like manner, although the generic and specific natures are never save in particular individuals, yet the intellect understands the specific and generic natures without understanding the individualizing principles: and this is to understand universals. And thus these two are not incompatible, namely that universals do not subsist outside the soul, and that the intellect, in understanding universals, understands things that are outside the soul. That the intellect understands the generic or specific nature apart from the individualizing principles results from the condition of the intelligible species received into it, for it is rendered immaterial by the active intellect, through being abstracted from matter and material conditions whereby a particular thing is individualized. Consequently the sensitive powers are unable to know universals: because they cannot receive an immaterial form, since they always receive in a corporeal organ.

Therefore it does not follow that the intelligible species is numerically one in this and that person who understand: for the result of this would be that the act of understanding in this and that person is numerically one, since operation follows the form which is the principle of the species. But in order that there be one thing understood, it is necessary that there be an image of one and the same thing. And this is possible if the intelligible species be numerically distinct: for nothing prevents several distinct images being made of one thing, and this is how one man is seen by several. Hence it is not incompatible with the intellect's knowledge of the universal that there be several intelligible species in several persons. Nor does it follow from this, if intelligible species be several in number and specifically the same, that they are not actually intelligible but only potentially, like other individual things. For individuality is not incompatible with actual intelligibility: since it must be admitted that both possible and active intellects are individual things, if we suppose them to be separate substances, not united to the body and subsistent of themselves, and yet they are intelligible. But it is materiality which is incompatible with intelligibility: a sign of which is that for forms of material things to be actually intelligible, they need to be abstracted from matter. Consequently in those things in which individualization is effected by particular signate matter, the things individualized are not actually intelligible; whereas if individualization is not the result of matter, nothing prevents things that are individual from being actually intelligible. Now intelligible species, like all other forms, are individualized by their subject which is the possible intellect. Wherefore, since the possible intellect is not material, it does not deprive of actual intelligibility the species which it individualizes.

Further. In sensible things, just as individuals are not actually intelligible if there be many in one species, for instance horses or men, so neither are those individuals which are alone in their species, as this particular sun or this particular moon. Now species are individualized in the same way by the possible intellect, whether there be several possible intellects or one; whereas they are not multiplied in the same way in the one species. Therefore it matters not, as regards the actual intelligibility of the species received into the possible intellect, whether there be one or several possible intellects in all.

Again. The possible intellect, according to the same Commentator, is the last in the order of intelligible substances, which in his opinion are several. Nor can it be denied that some of the higher substances are cognizant of the things which the possible intellect knows: since, as he says himself, the forms of the effects caused by the movement of a sphere are in the movers of the spheres. Hence it will still follow that, even if there be one possible intellect, the intelligible forms are multiplied in different intellects. And although we have stated that the intelligible species received into the possible intellect, is not that which is understood, but that whereby one understands, this does not prevent the intellect, by a kind of reflexion, from understanding itself and its act of intelligence, and the species whereby it understands. In fact it understands its act of intelligence in two ways: first in particular, for it understands that it understands in a particular instance; secondly, in general, in as much as it argues about the nature of its act. Consequently it understands both the intellect and the intelligible species in like manner in two ways: both by perceiving its own existence and that it has an intelligible species, which is a kind of particular knowledge, and by considering its own nature and that of the intelligible species, which is a kind of universal knowledge. In this latter sense we treat of the intellect and things intelligible in sciences.

From what has been said the solution to the third argument is also evident. For his statement that knowledge in the disciple and in the master is numerically one, is partly true and partly false. It is numerically one as regards the thing known, but not as regards the intelligible species whereby it is known, nor again as regards the habit itself of knowledge. And yet it does not follow that the master causes knowledge in the disciple in the same way as fire generates fire: since things are not in the same way generated by nature as by art. For fire generates fire naturally, by reducing matter from potentiality to the act of its form, whereas the master causes knowledge in his disciple after the manner of art, since to this purpose is assigned the art of demonstration which Aristotle teaches in the Posterior Analytics, or a demonstration is a syllogism that makes us know.[3]

It must, however, be observed, in accordance with Aristotle's teaching in 7 Metaph.,[4] that there are some arts in which the matter is not an active principle productive of the art's effect; such is the art of building, since in timber and stone there is not an active force tending to the production of a house, but merely a passive aptitude. On the other hand there is an art the matter of which is an active principle tending to produce the effect of the art; such is the medical art, since in the sick body there is an active principle conducive to health. Consequently the effect of an art of the first kind is never produced by nature but is always the result of the art. But the effect of an art of the second kind is the result both of art, and of nature without art: for many are healed by the action of nature without the art of medicine. In those things that can be done both by art and by nature, art copies nature;[5] for if a person is taken ill through a cold cause, nature cures him by heating. Now the art of teaching is like this art. For in him that is taught there is an active principle conducive to knowledge, namely the intellect, and those things which are naturally understood, namely first principles. Wherefore knowledge is acquired in two ways, both by discovery without teaching, and by teaching. Consequently the teacher begins to teach in the same way as the discoverer begins to discover, namely by offering to the disciple's consideration principles known by him, since all learning results from pre-existing knowledge;[6] and by drawing conclusions from those principles; and again by proposing sensible examples, from which there result, in the disciple's mind, the phantasms which are necessary that he may understand. And since the outward action of the teacher would have no effect, without the inward principle of knowledge, which is in us from God, hence among theologians it is said that man teaches by outward ministration, but God by inward operation: even so the physician is said to minister to nature when he heals. Accordingly knowledge is caused in the disciple by his master, not by way of natural action, but after the manner of art, as stated.

Further. Since the same Commentator places the habits of science in the passive intellect as their subject,[7] the unity of the possible intellect nowise causes numerical unity of knowledge in disciple and master. For it is evident that the passive intellect is not the same in different individuals, since it is a material power. Consequently this argument consistently with his position is not to the point.

  1. Averroes on 3 De Anima, text 5.
  2. Ch. lxxiii.
  3. I. ii. 4.
  4. D. 6, ix.
  5. 2 Phys. ii. 7.
  6. 1 Poster. i. 1.
  7. Cf. ch. lx.

Source: St. Thomas Aquinas, The Summa Contra Gentiles, trans. by The English Dominican Fathers from the latest Leonine Edition, Benzinger Brothers: New York, 1924.

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