SCG 2.76

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FROM the foregoing we may also conclude that neither is there one active intellect in all, as Alexander and Avicenna maintained, who do not hold that there is one possible intellect in all.

For since agent and recipient are mutually proportionate, it follows that to every patient there corresponds a proper agent. Now the possible intellect is compared to the active as the proper patient or recipient of the latter, since it is related to it as art to matter, as stated in 3 De Anima.[1] Hence if the possible intellect is part of the human soul, and multiplied according to the number of individuals, as we have shown,[2] the active intellect also will be the like, and not one for all.

Again. The active intellect makes the species to be actually intelligible, not that itself may understand by them, especially as a separate substance, since it is not in potentiality, but that the possible intellect may understand by them. Therefore it does not make them to be otherwise than as required by the possible intellect in order that it may understand. But it makes them to be such as it is itself, since every agent produces its like.[3] Therefore the active intellect is proportionate to the possible intellect: and consequently, since the possible intellect is a part of the soul, the active intellect is not a separate substance.

Moreover. Just as primary matter is perfected by natural forms which are outside the soul, so the possible intellect is perfected by forms actually understood. Now natural forms are received into primary matter, not by the action of only one separate substance, but by the action of a form of the same kind,--of a form, namely, that is in matter: even as this particular flesh is begotten through a form that is in this particular flesh and bones, as Aristotle proves in 7 Metaph.[4] Consequently if the possible intellect is a part of the soul and not a separate substance, as we have shown,[5] the active intellect, by whose action the intelligible species result therein, will not be a separate substance, but an active force of the soul.

Again. Plato held that knowledge in us is caused by ideas, which he affirmed to be separate substances; and Aristotle refutes this opinion in 1 Metaph.[6] Now it is clear that our knowledge depends on the active intellect as its first principle. If, then, the active intellect were a separate substance, there would be little or no difference between this opinion and Plato's which was refuted by the Philosopher.

Again. If the active intellect be a separate substance, its action must needs be continuous and uninterrupted: or at least we must say that it is not continued or interrupted at our will. Now its action is to make phantasms actually intelligible. Either, therefore, it will do this always, or not always. If not always, this will nevertheless not be at our discretion. Now, we understand actually when the phantasms are made actually intelligible. Consequently it follows that either we always understand, or that it is not in our power to understand actually.

Further. A separate substance stands in the same relation to all the phantasms that are in any men whatsoever: even as the sun stands in the same relation to all colours. Now sensible things are perceived by those who know as well as by those who are ignorant: and consequently the same phantasms are in both. Hence they will be made intelligible by the active intellect in either case: and consequently both will equally understand.

It may be said, however, that the active intellect for its own part is always active, but that the phantasms are not always made actually intelligible, but only when they are disposed thereto. Now, they are disposed thereto by the act of the cogitative power, the use of which is in our power. Consequently to understand actually is in our power. It is for this reason that not all men understand the things whereof they have the phantasms, since not all have the requisite act of the cogitative power, but only those who are instructed and accustomed.

Nevertheless this reply is seemingly not quite sufficient. For this disposition to understand, which is effected by the cogitative power, must either be a disposition of the possible intellect to receive intelligible forms emanating from the active intellect, as Avicenna maintains, or a disposition of the phantasms to be made actually intelligible, as Averroes and Alexander assert. Now, the former would seem improbable. Because the possible intellect by its very nature is in potentiality with regard to species actually intelligible, wherefore it stands in the same relation to them as a transparent body to light or to coloured images. And if a thing by its very nature is capable of receiving a certain form, it needs no further disposition to that form: unless perchance it contain contrary dispositions, as the matter of water is disposed to the form of air by the removal of cold and density. But there is nothing contrary in the possible intellect to prevent it receiving any intelligible species whatsoever: since the intelligible species even of contraries are not themselves contrary in the intellect, as Aristotle proves in 7 Metaph.,[7] for one is the reason for knowing the other. And the falsity which is incidental to the intellect's judgment in composition and division, results not from the presence in the intellect of certain things understood, but from its lack of certain things. Therefore the possible intellect, for its own part, requires no preparation in order to receive the intelligible species emanating from the active intellect.

Further. Colours which light has made actually visible, without fail impress their likeness on the diaphanous body and consequently on the sight. Consequently if the phantasms themselves on which the active intellect has shed its light did not impress their likeness on the possible intellect, but merely disposed it to receive them, the phantasms would not stand in the same relation to the possible intellect as colours to the sight, as Aristotle asserts.[8]

Again. According to this the phantasms, and consequently the senses would not be of themselves necessary for us to understand; but only accidentally, as it were inciting and preparing the possible intellect to receive. This is part of the Platonist theory, and contrary to the order which Aristotle assigns to the generation of art and science, in the first Book of Metaphysics[9] and the last Book of Posterior Analytics;[10] where he says that memory results from sensation; experience from many memories; from many memories the universal apprehension which is the beginning of science and art. This opinion of Avicenna, however, is in keeping with what he says about the generation of natural things.[11] For he holds that all lower agents, by their actions, prepare matter to receive the forms which emanate from a separate active intelligence into their respective matters. Hence also, for the same reason, he holds that the phantasms prepare the possible intellect; and that the intelligible forms emanate from a separate substance.

In like manner, if it be supposed that the active intellect is a separate substance, it seems unreasonable that the phantasms should be prepared by the cogitative power in order that they be actually intelligible and move the possible intellect. For this is seemingly in keeping with the opinion of those who say that the lower agents merely dispose to the ultimate perfection, and that this ultimate perfection is caused by a separate agent: which is contrary to the opinion of Aristotle in 7 Metaph.[12] For it would seem that the human soul is not less perfectly equipped for understanding than the lower things of nature for their proper operations.

Moreover. In this lower world the more noble effects are produced not by higher agents alone, but also require agents of their own genus, for the sun and man generate a man.[13] In like manner we observe that in other perfect animals, some of the lower animals are generated by the mere action of the sun, without an active principle of their own genus; for instance animals engendered of putrefaction. Now understanding is the most noble effect that takes place in this lower world. Therefore it is not enough to ascribe it to a remote agent, unless we suppose it to have also a proximate cause. This argument however does not avail against Avicenna, because he holds[14] that any animal can be generated without seed.

Again. The intention of the effect shows the agent. Wherefore animals engendered of putrefaction are not intended by a lower nature but only by a higher, since they are produced by a higher nature only: for which reason Aristotle (7 Metaph.)[15] says that they are effects of chance. Whereas animals that are produced from seed, are intended both by the higher and the lower nature. But this effect which is to abstract universal forms from the phantasms, is in our intention, and not merely in the intention of the remote agent. Therefore it follows that in us there must be a proximate principle of such an effect: and this is the active intellect. Therefore it is not a separate substance, but a power of our soul.

Again. The nature of every mover includes a principle sufficient for the natural operation thereof: and if this operation consists in an action, that nature includes an active principle, as appears in the powers of the nutritive soul of plants; while if this operation is a passion, it includes a passive principle, as appears in the sensitive powers of animals. Now man is the most perfect of all lower movers. And his proper and natural operation is to understand: which is not completed without some passion, in so far as the intellect is passive to the intelligible; nor again without action, in so far as the intellect makes things that are potentially intelligible to be intelligible actually. Therefore the respective principles of both, namely the active and possible intellects, must be in man's nature and neither of these must be separate, as to its being, from the soul of man.

Again. If the active intellect be a separate substance, it is evident that it is above man's nature. Now an operation which man performs by the power alone of a higher substance is a supernatural operation; such as the working of miracles, prophesying, and other like things which men do by God's favour. Since, then, man cannot understand except by the power of the active intellect, if the active intellect be a separate substance, it will follow that intelligence is not a natural operation to man: and consequently man cannot be defined as being intellectual and rational.

Further. Nothing operates save by a power that is in it formally: wherefore Aristotle (2 De Anima)[16] proves that the thing whereby we live and sense is a form and an act. Now both actions, namely of the active and possible intellects, are competent to man: for man abstracts from phantasms, and receives in his mind actual intelligibles; since otherwise we should not have become cognizant of these actions unless we experienced them in ourselves. Therefore the principles to which these actions are ascribed, namely the possible and active intellects, must be powers formally existing in us.

If, however, it be said that these actions are ascribed to man in so far as the aforesaid intellects are in conjunction with us, as Averroes says,[17] it has already been shown[18] that the possible intellect's conjunction with us, if it be a separate substance, such as he holds it to be, does not suffice for us to understand by its means. The same evidently applies to the active intellect. For the active intellect is to the intelligible species that are received into the possible intellect, as art to the artificial forms which art produces in matter, as appears from the example given by Aristotle in 3 De Anima.[19] Now art-forms do not acquire the action of art, but only a formal likeness, so that neither can the subject of these forms exercise the action of the craftsman. Therefore neither can man exercise the operation of the active intellect, through the intelligible species being made actual in him by the active intellect.

Again. A thing that cannot set about its proper operation unless it be moved by an outward principle, is moved to operate rather than moves itself: wherefore irrational animals are moved to operate rather than move themselves, since their every operation depends on the outward principle which moves them: for their sense, moved by the outward sensible, makes an impression on their imagination, and thus there is an orderly process in all their powers down to the motive powers. Now man's proper operation is intelligence, the first principle whereof is the active intellect which produces the intelligible species, to which in a sense the possible intellect is passive, and this being made actual moves the will. If, then, the active intellect is a substance outside man, all man's operation depends on an outward principle: and consequently he will not move himself but will be moved by another. Hence he will not be the master of his own operations, nor will he be deserving of praise or blame; and there will be an end to all moral science and social intercourse, which is absurd. Therefore the active intellect is not a substance separate from man.

  1. v. i.
  2. Ch. lxxiii.
  3. 1 De Gener. et Corrup. vii. 6.
  4. D. 6, viii. 7, 8.
  5. Ch. lix.
  6. ix.
  7. D. 6, vii. 5.
  8. 3 De Anima v. 1.
  9. i. 4.
  10. 2, xv. 5.
  11. Metaph, tr. ix. 5.
  12. D. 6, viii. 7. 8.
  13. 2 Phys. ii. 11.
  14. De Nat. Animal. 15, i.
  15. D. 6, vii. 4.
  16. ii. 12.
  17. Cf. ch. lix.
  18. Ibid.
  19. v. 1.

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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