Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the soul understands corporeal things through its essence. For Augustine says (De Trin. x, 5) that the soul "collects and lays hold of the images of bodies which are formed in the soul and of the soul: for in forming them it gives them something of its own substance." But the soul understands bodies by images of bodies. Therefore the soul knows bodies through its essence, which it employs for the formation of such images, and from which it forms them.

Objection 2: Further, the Philosopher says (De Anima iii, 8) that "the soul, after a fashion, is everything." Since, therefore, like is known by like, it seems that the soul knows corporeal things through itself.

Objection 3: Further, the soul is superior to corporeal creatures. Now lower things are in higher things in a more eminent way than in themselves, as Dionysius says (Coel. Hier. xii). Therefore all corporeal creatures exist in a more excellent way in the soul than in themselves. Therefore the soul can know corporeal creatures through its essence.

On the contrary, Augustine says (De Trin. ix, 3) that "the mind gathers knowledge of corporeal things through the bodily senses." But the soul itself cannot be known through the bodily senses. Therefore it does not know corporeal things through itself.

I answer that, The ancient philosophers held that the soul knows bodies through its essence. For it was universally admitted that "like is known by like." But they thought that the form of the thing known is in the knower in the same mode as in the thing known. The Platonists however were of a contrary opinion. For Plato, having observed that the intellectual soul has an immaterial nature, and an immaterial mode of knowledge, held that the forms of things known subsist immaterially. While the earlier natural philosophers, observing that things known are corporeal and material, held that things known must exist materially even in the soul that knows them. And therefore, in order to ascribe to the soul a knowledge of all things, they held that it has the same nature in common with all. And because the nature of a result is determined by its principles, they ascribed to the soul the nature of a principle; so that those who thought fire to be the principle of all, held that the soul had the nature of fire; and in like manner as to air and water. Lastly, Empedocles, who held the existence of our four material elements and two principles of movement, said that the soul was composed of these. Consequently, since they held that things exist in the soul materially, they maintained that all the soul's knowledge is material, thus failing to discern intellect from sense.

But this opinion will not hold. First, because in the material principle of which they spoke, the various results do not exist save in potentiality. But a thing is not known according as it is in potentiality, but only according as it is in act, as is shown Metaph. ix (Did. viii, 9): wherefore neither is a power known except through its act. It is therefore insufficient to ascribe to the soul the nature of the principles in order to explain the fact that it knows all, unless we further admit in the soul natures and forms of each individual result, for instance, of bone, flesh, and the like; thus does Aristotle argue against Empedocles (De Anima i, 5). Secondly, because if it were necessary for the thing known to exist materially in the knower, there would be no reason why things which have a material existence outside the soul should be devoid of knowledge; why, for instance, if by fire the soul knows fire, that fire also which is outside the soul should not have knowledge of fire.

We must conclude, therefore, that material things known must needs exist in the knower, not materially, but immaterially. The reason of this is, because the act of knowledge extends to things outside the knower: for we know things even that are external to us. Now by matter the form of a thing is determined to some one thing. Wherefore it is clear that knowledge is in inverse ratio of materiality. And consequently things that are not receptive of forms save materially, have no power of knowledge whatever---such as plants, as the Philosopher says (De Anima ii, 12). But the more immaterially a thing receives the form of the thing known, the more perfect is its knowledge. Therefore the intellect which abstracts the species not only from matter, but also from the individuating conditions of matter, has more perfect knowledge than the senses, which receive the form of the thing known, without matter indeed, but subject to material conditions. Moreover, among the senses, sight has the most perfect knowledge, because it is the least material, as we have remarked above (Question 78, Article 3): while among intellects the more perfect is the more immaterial.

It is therefore clear from the foregoing, that if there be an intellect which knows all things by its essence, then its essence must needs have all things in itself immaterially; thus the early philosophers held that the essence of the soul, that it may know all things, must be actually composed of the principles of all material things. Now this is proper to God, that His Essence comprise all things immaterially as effects pre-exist virtually in their cause. God alone, therefore, understands all things through His Essence: but neither the human soul nor the angels can do so.

Reply to Objection 1: Augustine in that passage is speaking of an imaginary vision, which takes place through the image of bodies. To the formation of such images the soul gives part of its substance, just as a subject is given in order to be informed by some form. In this way the soul makes such images from itself; not that the soul or some part of the soul be turned into this or that image; but just as we say that a body is made into something colored because of its being informed with color. That this is the sense, is clear from what follows. For he says that the soul "keeps something"---namely, not informed with such image---"which is able freely to judge of the species of these images": and that this is the "mind" or "intellect." And he says that the part which is informed with these images---namely, the imagination---is "common to us and beasts."

Reply to Objection 2: Aristotle did not hold that the soul is actually composed of all things, as did the earlier philosophers; he said that the soul is all things, "after a fashion," forasmuch as it is in potentiality to all---through the senses, to all things sensible---through the intellect, to all things intelligible.

Reply to Objection 3: Every creature has a finite and determinate essence. Wherefore although the essence of the higher creature has a certain likeness to the lower creature, forasmuch as they have something in common generically, yet it has not a complete likeness thereof, because it is determined to a certain species other than the species of the lower creature. But the Divine Essence is a perfect likeness of all, whatsoever may be found to exist in things created, being the universal principle of all.

Articulus 2

Argumentum 1

Ad secundum sic proceditur. Videtur quod anima per essentiam suam corporalia intelligat.

Dicit enim Augustinus, X de Trin., quod anima imagines corporum convolvit et rapit factas in semetipsa de semetipsa, dat enim eis formandis quiddam substantiae suae.

Sed per similitudines corporum corpora intelligit.

Ergo per essentiam suam, quam dat formandis talibus similitudinibus, et de qua eas format, cognoscit corporalia.

Argumentum 2

Praeterea, philosophus dicit, in III de anima, quod anima quodammodo est omnia.

Cum ergo simile simili cognoscatur, videtur quod anima per seipsam corporalia cognoscat.

Argumentum 3

Praeterea, anima est superior corporalibus creaturis. Inferiora autem sunt in superioribus eminentiori modo quam in seipsis, ut dionysius dicit.

Ergo omnes creaturae corporeae nobiliori modo existunt in ipsa substantia animae quam in seipsis. Per suam ergo substantiam potest creaturas corporeas cognoscere.

Sed Contra

Sed contra est quod Augustinus dicit, IX de Trin., quod mens corporearum rerum notitias per sensus corporis colligit.

Ipsa autem anima non est cognoscibilis per corporis sensus.

Non ergo cognoscit corporea per suam substantiam.

Corpus

Respondeo dicendum quod antiqui philosophi posuerunt quod anima per suam essentiam cognoscit corpora. Hoc enim animis omnium communiter inditum fuit, quod simile simili cognoscitur.

Existimabant autem quod forma cogniti sit in cognoscente eo modo quo est in re cognita.

E contrario tamen Platonici posuerunt.

Plato enim, quia perspexit intellectualem animam immaterialem esse et immaterialiter cognoscere, posuit formas rerum cognitarum immaterialiter subsistere.

Priores vero naturales, quia considerabant res cognitas esse corporeas et materiales, posuerunt oportere res cognitas etiam in anima cognoscente materialiter esse. Et ideo, ut animae attribuerent omnium cognitionem, posuerunt eam habere naturam communem cum omnibus.

Et quia natura principiatorum ex principiis constituitur, attribuerunt animae naturam principii, ita quod qui dixit principium omnium esse ignem, posuit animam esse de natura ignis; et similiter de aere et aqua.

Empedocles autem, qui posuit quatuor elementa materialia et duo moventia, ex his etiam dixit animam esse constitutam. Et ita, cum res materialiter in anima ponerent, posuerunt omnem cognitionem animae materialem esse, non discernentes inter intellectum et sensum. Sed haec opinio improbatur. Primo quidem, quia in materiali principio, de quo loquebantur, non existunt principiata nisi in potentia.

Non autem cognoscitur aliquid secundum quod est in potentia, sed solum secundum quod est actu, ut patet in IX metaphys., unde nec ipsa potentia cognoscitur nisi per actum. Sic igitur non sufficeret attribuere animae principiorum naturam ad hoc quod omnia cognosceret, nisi inessent ei naturae et formae singulorum effectuum, puta ossis et carnis et aliorum huiusmodi; ut Aristoteles contra empedoclem argumentatur in I de anima.

Secundo quia, si oporteret rem cognitam materialiter in cognoscente existere, nulla ratio esset quare res quae materialiter extra animam subsistunt, cognitione carerent, puta, si anima igne cognoscit ignem, et ignis etiam qui est extra animam, ignem cognosceret. Relinquitur ergo quod oportet materialia cognita in cognoscente existere non materialiter, sed magis immaterialiter. Et huius ratio est, quia actus cognitionis se extendit ad ea quae sunt extra cognoscentem, cognoscimus enim etiam ea quae extra nos sunt. Per materiam autem determinatur forma rei ad aliquid unum. Unde manifestum est quod ratio cognitionis ex opposito se habet ad rationem materialitatis.

Et ideo quae non recipiunt formas nisi materialiter, nullo modo sunt cognoscitiva, sicut plantae; ut dicitur in II libro de anima.

Quanto autem aliquid immaterialius habet formam rei cognitae, tanto perfectius cognoscit. Unde et intellectus, qui abstrahit speciem non solum a materia, sed etiam a materialibus conditionibus individuantibus, perfectius cognoscit quam sensus, qui accipit formam rei cognitae sine materia quidem, sed cum materialibus conditionibus. Et inter ipsos sensus, visus est magis cognoscitivus, quia est minus materialis, ut supra dictum est.

Et inter ipsos intellectus, tanto quilibet est perfectior, quanto immaterialior. Ex his ergo patet quod, si aliquis intellectus est qui per essentiam suam cognoscit omnia, oportet quod essentia eius habeat in se immaterialiter omnia; sicut antiqui posuerunt essentiam animae actu componi ex principiis omnium materialium, ut cognosceret omnia. Hoc autem est proprium dei, ut sua essentia sit immaterialiter comprehensiva omnium, prout effectus virtute praeexistunt in causa. Solus igitur deus per essentiam suam omnia intelligit; non autem anima humana, neque etiam Angelus.

Ad 1

Ad primum ergo dicendum quod Augustinus ibi loquitur de visione imaginaria, quae fit per imagines corporum. Quibus imaginibus formandis dat anima aliquid suae substantiae, sicut subiectum datur ut informetur per aliquam formam. Et sic de seipsa facit huiusmodi imagines, non quod anima vel aliquid animae convertatur, ut sit haec vel illa imago; sed sicut dicitur de corpore fieri aliquid coloratum, prout informatur colore.

Et hic sensus apparet ex his quae sequuntur.

Dicit enim quod servat aliquid, scilicet non formatum tali imagine, quod libere de specie talium imaginum iudicet, et hoc dicit esse mentem vel intellectum. Partem autem quae informatur huiusmodi imaginibus scilicet imaginativam, dicit esse communem nobis et bestiis.

Ad 2

Ad secundum dicendum quod Aristoteles non posuit animam esse actu compositam ex omnibus, sicut antiqui naturales; sed dixit quodammodo animam esse omnia, inquantum est in potentia ad omnia; per sensum quidem ad sensibilia, per intellectum vero ad intelligibilia.

Ad 3

Ad tertium dicendum quod quaelibet creatura habet esse finitum et determinatum. Unde essentia superioris creaturae, etsi habeat quandam similitudinem inferioris creaturae prout communicant in aliquo genere, non tamen complete habet similitudinem illius, quia determinatur ad aliquam speciem, praeter quam est species inferioris creaturae. Sed essentia dei est perfecta similitudo omnium quantum ad omnia quae in rebus inveniuntur, sicut universale principium omnium.