Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that there is no active intellect. For as the senses are to things sensible, so is our intellect to things intelligible. But because sense is in potentiality to things sensible, the sense is not said to be active, but only passive. Therefore, since our intellect is in potentiality to things intelligible, it seems that we cannot say that the intellect is active, but only that it is passive.

Objection 2: Further, if we say that also in the senses there is something active, such as light: on the contrary, light is required for sight, inasmuch as it makes the medium to be actually luminous; for color of its own nature moves the luminous medium. But in the operation of the intellect there is no appointed medium that has to be brought into act. Therefore there is no necessity for an active intellect.

Objection 3: Further, the likeness of the agent is received into the patient according to the nature of the patient. But the passive intellect is an immaterial power. Therefore its immaterial nature suffices for forms to be received into it immaterially. Now a form is intelligible in act from the very fact that it is immaterial. Therefore there is no need for an active intellect to make the species actually intelligible.

On the contrary, The Philosopher says (De Anima iii, 5), "As in every nature, so in the soul is there something by which it becomes all things, and something by which it makes all things." Therefore we must admit an active intellect.

I answer that, According to the opinion of Plato, there is no need for an active intellect in order to make things actually intelligible; but perhaps in order to provide intellectual light to the intellect, as will be explained farther on (Article 4). For Plato supposed that the forms of natural things subsisted apart from matter, and consequently that they are intelligible: since a thing is actually intelligible from the very fact that it is immaterial. And he called such forms "species or ideas"; from a participation of which, he said that even corporeal matter was formed, in order that individuals might be naturally established in their proper genera and species: and that our intellect was formed by such participation in order to have knowledge of the genera and species of things. But since Aristotle did not allow that forms of natural things exist apart from matter, and as forms existing in matter are not actually intelligible; it follows that the natures of forms of the sensible things which we understand are not actually intelligible. Now nothing is reduced from potentiality to act except by something in act; as the senses as made actual by what is actually sensible. We must therefore assign on the part of the intellect some power to make things actually intelligible, by abstraction of the species from material conditions. And such is the necessity for an active intellect.

Reply to Objection 1: Sensible things are found in act outside the soul; and hence there is no need for an active sense. Wherefore it is clear that in the nutritive part all the powers are active, whereas in the sensitive part all are passive: but in the intellectual part, there is something active and something passive.

Reply to Objection 2: There are two opinions as to the effect of light. For some say that light is required for sight, in order to make colors actually visible. And according to this the active intellect is required for understanding, in like manner and for the same reason as light is required for seeing. But in the opinion of others, light is required for sight; not for the colors to become actually visible; but in order that the medium may become actually luminous, as the Commentator says on De Anima ii. And according to this, Aristotle's comparison of the active intellect to light is verified in this, that as it is required for understanding, so is light required for seeing; but not for the same reason.

Reply to Objection 3: If the agent pre-exist, it may well happen that its likeness is received variously into various things, on account of their dispositions. But if the agent does not pre-exist, the disposition of the recipient has nothing to do with the matter. Now the intelligible in act is not something existing in nature; if we consider the nature of things sensible, which do not subsist apart from matter. And therefore in order to understand them, the immaterial nature of the passive intellect would not suffice but for the presence of the active intellect which makes things actually intelligible by way of abstraction.

Articulus 3

Argumentum 1

Ad tertium sic proceditur. Videtur quod non sit ponere intellectum agentem. Sicut enim se habet sensus ad sensibilia, ita se habet intellectus noster ad intelligibilia. Sed quia sensus est in potentia ad sensibilia non ponitur sensus agens, sed sensus patiens tantum. Ergo, cum intellectus noster sit in potentia ad intelligibilia, videtur quod non debeat poni intellectus agens, sed possibilis tantum.

Argumentum 2

Praeterea, si dicatur quod in sensu etiam est aliquod agens, sicut lumen, contra, lumen requiritur ad visum inquantum facit medium lucidum in actu, nam color ipse secundum se est motivus lucidi. Sed in operatione intellectus non ponitur aliquod medium quod necesse sit fieri in actu. Ergo non est necessarium ponere intellectum agentem.

Argumentum 3

Praeterea, similitudo agentis recipitur in patiente secundum modum patientis. Sed intellectus possibilis est virtus immaterialis.

Ergo immaterialitas eius sufficit ad hoc quod recipiantur in eo formae immaterialiter. Sed ex hoc ipso aliqua forma est intelligibilis in actu, quod est immaterialis.

Ergo nulla necessitas est ponere intellectum agentem, ad hoc quod faciat species intelligibiles in actu.

Sed Contra

Sed contra est quod philosophus dicit, in III de anima, quod sicut in omni natura ita et in anima est aliquid quo est omnia fieri, et aliquid quo est omnia facere.

Est ergo ponere intellectum agentem.

Corpus

Respondeo dicendum quod, secundum opinionem Platonis, nulla necessitas erat ponere intellectum agentem ad faciendum intelligibilia in actu; sed forte ad praebendum lumen intelligibile intelligenti, ut infra dicetur.

Posuit enim Plato formas rerum naturalium sine materia subsistere, et per consequens eas intelligibiles esse, quia ex hoc est aliquid intelligibile actu, quod est immateriale. Et huiusmodi vocabat species, sive ideas, ex quarum participatione dicebat etiam materiam corporalem formari, ad hoc quod individua naturaliter constituerentur in propriis generibus et speciebus; et intellectus nostros, ad hoc quod de generibus et speciebus rerum scientiam haberent.

Sed quia Aristoteles non posuit formas rerum naturalium subsistere sine materia; formae autem in materia existentes non sunt intelligibiles actu, sequebatur quod naturae seu formae rerum sensibilium, quas intelligimus, non essent intelligibiles actu. Nihil autem reducitur de potentia in actum, nisi per aliquod ens actu, sicut sensus fit in actu per sensibile in actu. Oportebat igitur ponere aliquam virtutem ex parte intellectus, quae faceret intelligibilia in actu, per abstractionem specierum a conditionibus materialibus.

Et haec est necessitas ponendi intellectum agentem.

Ad 1

Ad primum ergo dicendum quod sensibilia inveniuntur actu extra animam, et ideo non oportuit ponere sensum agentem. Et sic patet quod in parte nutritiva omnes potentiae sunt activae; in parte autem sensitiva, omnes passivae; in parte vero intellectiva est aliquid activum, et aliquid passivum.

Ad 2

Ad secundum dicendum quod circa effectum luminis est duplex opinio. Quidam enim dicunt quod lumen requiritur ad visum, ut faciat colores actu visibiles. Et secundum hoc, similiter requiritur, et propter idem, intellectus agens ad intelligendum, propter quod lumen ad videndum. Secundum alios vero, lumen requiritur ad videndum, non propter colores, ut fiant actu visibiles; sed ut medium fiat actu lucidum, ut Commentator dicit in II de anima.

Et secundum hoc, similitudo qua Aristoteles assimilat intellectum agentem lumini, attenditur quantum ad hoc, quod sicut hoc est necessarium ad videndum, ita illud ad intelligendum; sed non propter idem.

Ad 3

Ad tertium dicendum quod, supposito agente, bene contingit diversimode recipi eius similitudinem in diversis propter eorum dispositionem diversam. Sed si agens non praeexistit, nihil ad hoc faciet dispositio recipientis. Intelligibile autem in actu non est aliquid existens in rerum natura, quantum ad naturam rerum sensibilium, quae non subsistunt praeter materiam. Et ideo ad intelligendum non sufficeret immaterialitas intellectus possibilis, nisi adesset intellectus agens, qui faceret intelligibilia in actu per modum abstractionis.