Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the active intellect is not something in the soul. For the effect of the active intellect is to give light for the purpose of understanding. But this is done by something higher than the soul: according to Jn. 1:9, "He was the true light that enlighteneth every man coming into this world." Therefore the active intellect is not something in the soul.

Objection 2: Further, the Philosopher (De Anima iii, 5) says of the active intellect, "that it does not sometimes understand and sometimes not understand." But our soul does not always understand: sometimes it understands, sometimes it does not understand. Therefore the active intellect is not something in our soul.

Objection 3: Further, agent and patient suffice for action. If, therefore, the passive intellect, which is a passive power, is something belonging to the soul; and also the active intellect, which is an active power: it follows that a man would always be able to understand when he wished, which is clearly false. Therefore the active intellect is not something in our soul.

Objection 4: Further, the Philosopher (De Anima iii, 5) says that the active intellect is a "substance in actual being." But nothing can be in potentiality and in act with regard to the same thing. If, therefore, the passive intellect, which is in potentiality to all things intelligible, is something in the soul, it seems impossible for the active intellect to be also something in our soul.

Objection 5: Further, if the active intellect is something in the soul, it must be a power. For it is neither a passion nor a habit; since habits and passions are not in the nature of agents in regard to the passivity of the soul; but rather passion is the very action of the passive power; while habit is something which results from acts. But every power flows from the essence of the soul. It would therefore follow that the active intellect flows from the essence of the soul. And thus it would not be in the soul by way of participation from some higher intellect: which is unfitting. Therefore the active intellect is not something in our soul.

On the contrary, The Philosopher says (De Anima iii, 5), that "it is necessary for these differences," namely, the passive and active intellect, "to be in the soul."

I answer that, The active intellect, of which the Philosopher speaks, is something in the soul. In order to make this evident, we must observe that above the intellectual soul of man we must needs suppose a superior intellect, from which the soul acquires the power of understanding. For what is such by participation, and what is mobile, and what is imperfect always requires the pre-existence of something essentially such, immovable and perfect. Now the human soul is called intellectual by reason of a participation in intellectual power; a sign of which is that it is not wholly intellectual but only in part. Moreover it reaches to the understanding of truth by arguing, with a certain amount of reasoning and movement. Again it has an imperfect understanding; both because it does not understand everything, and because, in those things which it does understand, it passes from potentiality to act. Therefore there must needs be some higher intellect, by which the soul is helped to understand.

Wherefore some held that this intellect, substantially separate, is the active intellect, which by lighting up the phantasms as it were, makes them to be actually intelligible. But, even supposing the existence of such a separate active intellect, it would still be necessary to assign to the human soul some power participating in that superior intellect, by which power the human soul makes things actually intelligible. Just as in other perfect natural things, besides the universal active causes, each one is endowed with its proper powers derived from those universal causes: for the sun alone does not generate man; but in man is the power of begetting man: and in like manner with other perfect animals. Now among these lower things nothing is more perfect than the human soul. Wherefore we must say that in the soul is some power derived from a higher intellect, whereby it is able to light up the phantasms. And we know this by experience, since we perceive that we abstract universal forms from their particular conditions, which is to make them actually intelligible. Now no action belongs to anything except through some principle formally inherent therein; as we have said above of the passive intellect (Question 76, Article 1). Therefore the power which is the principle of this action must be something in the soul. For this reason Aristotle (De Anima iii, 5) compared the active intellect to light, which is something received into the air: while Plato compared the separate intellect impressing the soul to the sun, as Themistius says in his commentary on De Anima iii. But the separate intellect, according to the teaching of our faith, is God Himself, Who is the soul's Creator, and only beatitude; as will be shown later on (Question 90, Article 3; 1.2, Question 3, Article 7). Wherefore the human soul derives its intellectual light from Him, according to Ps. 4:7, "The light of Thy countenance, O Lord, is signed upon us."

Reply to Objection 1: That true light enlightens as a universal cause, from which the human soul derives a particular power, as we have explained.

Reply to Objection 2: The Philosopher says those words not of the active intellect, but of the intellect in act: of which he had already said: "Knowledge in act is the same as the thing." Or, if we refer those words to the active intellect, then they are said because it is not owing to the active intellect that sometimes we do, and sometimes we do not understand, but to the intellect which is in potentiality.

Reply to Objection 3: If the relation of the active intellect to the passive were that of the active object to a power, as, for instance, of the visible in act to the sight; it would follow that we could understand all things instantly, since the active intellect is that which makes all things (in act). But now the active intellect is not an object, rather is it that whereby the objects are made to be in act: for which, besides the presence of the active intellect, we require the presence of phantasms, the good disposition of the sensitive powers, and practice in this sort of operation; since through one thing understood, other things come to be understood, as from terms are made propositions, and from first principles, conclusions. From this point of view it matters not whether the active intellect is something belonging to the soul, or something separate from the soul.

Reply to Objection 4: The intellectual soul is indeed actually immaterial, but it is in potentiality to determinate species. On the contrary, phantasms are actual images of certain species, but are immaterial in potentiality. Wherefore nothing prevents one and the same soul, inasmuch as it is actually immaterial, having one power by which it makes things actually immaterial, by abstraction from the conditions of individual matter: which power is called the "active intellect"; and another power, receptive of such species, which is called the "passive intellect" by reason of its being in potentiality to such species.

Reply to Objection 5: Since the essence of the soul is immaterial, created by the supreme intellect, nothing prevents that power which it derives from the supreme intellect, and whereby it abstracts from matter, flowing from the essence of the soul, in the same way as its other powers.

Articulus 4

Argumentum 1

Ad quartum sic proceditur. Videtur quod intellectus agens non sit aliquid animae nostrae. Intellectus enim agentis effectus est illuminare ad intelligendum. Sed hoc fit per aliquid quod est altius anima; secundum illud Ioan. I, erat lux vera, quae illuminat omnem hominem venientem in hunc mundum.

Ergo videtur quod intellectus agens non sit aliquid animae.

Argumentum 2

Praeterea, philosophus, in III de anima, attribuit intellectui agenti quod non aliquando intelligit et aliquando non intelligit.

Sed anima nostra non semper intelligit; sed aliquando intelligit et aliquando non intelligit. Ergo intellectus agens non est aliquid animae nostrae.

Argumentum 3

Praeterea, agens et patiens sufficiunt ad agendum. Si igitur intellectus possibilis est aliquid animae nostrae, qui est virtus passiva, et similiter intellectus agens, qui est virtus activa; sequitur quod homo semper poterit intelligere cum voluerit, quod patet esse falsum.

Non est ergo intellectus agens aliquid animae nostrae.

Argumentum 4

Praeterea, philosophus dicit, in III de anima, quod intellectus agens est substantia actu ens.

Nihil autem est respectu eiusdem in actu et in potentia. Si ergo intellectus possibilis, qui est in potentia ad omnia intelligibilia, est aliquid animae nostrae; videtur impossibile quod intellectus agens sit aliquid animae nostrae.

Argumentum 5

Praeterea, si intellectus agens est aliquid animae nostrae, oportet quod sit aliqua potentia. Non est enim nec passio nec habitus, nam habitus et passiones non habent rationem agentis respectu passionum animae; sed magis passio est ipsa actio potentiae passivae, habitus autem est aliquid quod ex actibus consequitur. Omnis autem potentia fluit ab essentia animae.

Sequeretur ergo quod intellectus agens ab essentia animae procederet. Et sic non inesset animae per participationem ab aliquo superiori intellectu, quod est inconveniens.

Non ergo intellectus agens est aliquid animae nostrae.

Sed Contra

Sed contra est quod philosophus dicit, III de anima quod necesse est in anima has esse differentias, scilicet intellectum possibilem, et agentem.

Corpus

Respondeo dicendum quod intellectus agens de quo philosophus loquitur, est aliquid animae. Ad cuius evidentiam, considerandum est quod supra animam intellectivam humanam necesse est ponere aliquem superiorem intellectum, a quo anima virtutem intelligendi obtineat. Semper enim quod participat aliquid, et quod est mobile, et quod est imperfectum, praeexigit ante se aliquid quod est per essentiam suam tale, et quod est immobile et perfectum. Anima autem humana intellectiva dicitur per participationem intellectualis virtutis, cuius signum est, quod non tota est intellectiva, sed secundum aliquam sui partem.

Pertingit etiam ad intelligentiam veritatis cum quodam discursu et motu, arguendo. Habet etiam imperfectam intelligentiam, tum quia non omnia intelligit; tum quia in his quae intelligit, de potentia procedit ad actum. Oportet ergo esse aliquem altiorem intellectum, quo anima iuvetur ad intelligendum.

Posuerunt ergo quidam hunc intellectum secundum substantiam separatum, esse intellectum agentem, qui quasi illustrando phantasmata, facit ea intelligibilia actu.

Sed, dato quod sit aliquis talis intellectus agens separatus, nihilominus tamen oportet ponere in ipsa anima humana aliquam virtutem ab illo intellectu superiori participatam, per quam anima humana facit intelligibilia in actu. Sicut et in aliis rebus naturalibus perfectis, praeter universales causas agentes, sunt propriae virtutes inditae singulis rebus perfectis, ab universalibus agentibus derivatae, non enim solus sol generat hominem, sed est in homine virtus generativa hominis; et similiter in aliis animalibus perfectis. Nihil autem est perfectius in inferioribus rebus anima humana. Unde oportet dicere quod in ipsa sit aliqua virtus derivata a superiori intellectu, per quam possit phantasmata illustrare. Et hoc experimento cognoscimus, dum percipimus nos abstrahere formas universales a conditionibus particularibus, quod est facere actu intelligibilia. Nulla autem actio convenit alicui rei, nisi per aliquod principium formaliter ei inhaerens; ut supra dictum est, cum de intellectu possibili ageretur.

Ergo oportet virtutem quae est principium huius actionis, esse aliquid in anima.

Et ideo Aristoteles comparavit intellectum agentem lumini, quod est aliquid receptum in aere.

Plato autem intellectum separatum imprimentem in animas nostras, comparavit soli; ut themistius dicit in commentario tertii de anima.

Sed intellectus separatus, secundum nostrae fidei documenta, est ipse deus, qui est creator animae, et in quo solo beatificatur, ut infra patebit.

Unde ab ipso anima humana lumen intellectuale participat, secundum illud Psalmi IV, signatum est super nos lumen vultus tui, domine.

Ad 1

Ad primum ergo dicendum quod illa lux vera illuminat sicut causa universalis, a qua anima humana participat quandam particularem virtutem, ut dictum est.

Ad 2

Ad secundum dicendum quod philosophus illa verba non dicit de intellectu agente, sed de intellectu in actu. Unde supra de ipso praemiserat, idem autem est secundum actum scientia rei.

Vel, si intelligatur de intellectu agente, hoc dicitur quia non est ex parte intellectus agentis hoc quod quandoque intelligimus et quandoque non intelligimus; sed ex parte intellectus qui est in potentia.

Ad 3

Ad tertium dicendum quod, si intellectus agens compararetur ad intellectum possibilem ut obiectum agens ad potentiam, sicut visibile in actu ad visum; sequeretur quod statim omnia intelligeremus, cum intellectus agens sit quo est omnia facere.

Nunc autem non se habet ut obiectum, sed ut faciens obiecta in actu, ad quod requiritur, praeter praesentiam intellectus agentis, praesentia phantasmatum, et bona dispositio virium sensitivarum, et exercitium in huiusmodi opere; quia per unum intellectum fiunt etiam alia intellecta, sicut per terminos propositiones, et per prima principia conclusiones. Et quantum ad hoc, non differt utrum intellectus agens sit aliquid animae, vel aliquid separatum.

Ad 4

Ad quartum dicendum quod anima intellectiva est quidem actu immaterialis, sed est in potentia ad determinatas species rerum.

Phantasmata autem, e converso, sunt quidem actu similitudines specierum quarundam, sed sunt potentia immaterialia. Unde nihil prohibet unam et eandem animam, inquantum est immaterialis in actu, habere aliquam virtutem per quam faciat immaterialia in actu abstrahendo a conditionibus individualis materiae, quae quidem virtus dicitur intellectus agens; et aliam virtutem receptivam huiusmodi specierum, quae dicitur intellectus possibilis, inquantum est in potentia ad huiusmodi species.

Ad 5

Ad quintum dicendum quod, cum essentia animae sit immaterialis, a supremo intellectu creata, nihil prohibet virtutem quae a supremo intellectu participatur, per quam abstrahit a materia, ab essentia ipsius procedere, sicut et alias eius potentias.