Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the intellectual soul knows itself by its own essence. For Augustine says (De Trin. ix, 3), that "the mind knows itself, because it is incorporeal."

Objection 2: Further, both angels and human souls belong to the genus of intellectual substance. But an angel understands itself by its own essence. Therefore likewise does the human soul.

Objection 3: Further, "in things void of matter, the intellect and that which is understood are the same" (De Anima iii, 4). But the human mind is void of matter, not being the act of a body as stated above (Question 76, Article 1). Therefore the intellect and its object are the same in the human mind; and therefore the human mind understands itself by its own essence.

On the contrary, It is said (De Anima iii, 4) that "the intellect understands itself in the same way as it understands other things." But it understands other things, not by their essence, but by their similitudes. Therefore it does not understand itself by its own essence.

I answer that, Everything is knowable so far as it is in act, and not, so far as it is in potentiality (Metaph. ix, Did. viii, 9): for a thing is a being, and is true, and therefore knowable, according as it is actual. This is quite clear as regards sensible things, for the eye does not see what is potentially, but what is actually colored. In like manner it is clear that the intellect, so far as it knows material things, does not know save what is in act: and hence it does not know primary matter except as proportionate to form, as is stated Phys. i, 7. Consequently immaterial substances are intelligible by their own essence according as each one is actual by its own essence.

Therefore it is that the Essence of God, the pure and perfect act, is simply and perfectly in itself intelligible; and hence God by His own Essence knows Himself, and all other things also. The angelic essence belongs, indeed, to the genus of intelligible things as "act," but not as a "pure act," nor as a "complete act," and hence the angel's act of intelligence is not completed by his essence. For although an angel understands himself by his own essence, still he cannot understand all other things by his own essence; for he knows things other than himself by their likenesses. Now the human intellect is only a potentiality in the genus of intelligible beings, just as primary matter is a potentiality as regards sensible beings; and hence it is called "possible" . Therefore in its essence the human mind is potentially understanding. Hence it has in itself the power to understand, but not to be understood, except as it is made actual. For even the Platonists asserted than an order of intelligible beings existed above the order of intellects, forasmuch as the intellect understands only by participation of the intelligible; for they said that the participator is below what it participates. If, therefore, the human intellect, as the Platonists held, became actual by participating separate intelligible forms, it would understand itself by such participation of incorporeal beings. But as in this life our intellect has material and sensible things for its proper natural object, as stated above (Question 84, Article 7), it understands itself according as it is made actual by the species abstracted from sensible things, through the light of the active intellect, which not only actuates the intelligible things themselves, but also, by their instrumentality, actuates the passive intellect. Therefore the intellect knows itself not by its essence, but by its act. This happens in two ways: In the first place, singularly, as when Socrates or Plato perceives that he has an intellectual soul because he perceives that he understands. In the second place, universally, as when we consider the nature of the human mind from knowledge of the intellectual act. It is true, however, that the judgment and force of this knowledge, whereby we know the nature of the soul, comes to us according to the derivation of our intellectual light from the Divine Truth which contains the types of all things as above stated (Question 84, Article 5). Hence Augustine says (De Trin. ix, 6): "We gaze on the inviolable truth whence we can as perfectly as possible define, not what each man's mind is, but what it ought to be in the light of the eternal types." There is, however, a difference between these two kinds of knowledge, and it consists in this, that the mere presence of the mind suffices for the first; the mind itself being the principle of action whereby it perceives itself, and hence it is said to know itself by its own presence. But as regards the second kind of knowledge, the mere presence of the mind does not suffice, and there is further required a careful and subtle inquiry. Hence many are ignorant of the soul's nature, and many have erred about it. So Augustine says (De Trin. x, 9), concerning such mental inquiry: "Let the mind strive not to see itself as if it were absent, but to discern itself as present"---i.e. to know how it differs from other things; which is to know its essence and nature.

Reply to Objection 1: The mind knows itself by means of itself, because at length it acquires knowledge of itself, though led thereto by its own act: because it is itself that it knows since it loves itself, as he says in the same passage. For a thing can be called self-evident in two ways, either because we can know it by nothing else except itself, as first principles are called self-evident; or because it is not accidentally knowable, as color is visible of itself, whereas substance is visible by its accident.

Reply to Objection 2: The essence of an angel is an act in the genus of intelligible things, and therefore it is both intellect and the thing understood. Hence an angel apprehends his own essence through itself: not so the human mind, which is either altogether in potentiality to intelligible things---as is the passive intellect---or is the act of intelligible things abstracted from the phantasms---as is the active intellect.

Reply to Objection 3: This saying of the Philosopher is universally true in every kind of intellect. For as sense in act is the sensible in act, by reason of the sensible likeness which is the form of sense in act, so likewise the intellect in act is the object understood in act, by reason of the likeness of the thing understood, which is the form of the intellect in act. So the human intellect, which becomes actual by the species of the object understood, is itself understood by the same species as by its own form. Now to say that in "things without matter the intellect and what is understood are the same," is equal to saying that "as regards things actually understood the intellect and what is understood are the same." For a thing is actually understood in that it is immaterial. But a distinction must be drawn: since the essences of some things are immaterial---as the separate substances called angels, each of which is understood and understands, whereas there are other things whose essences are not wholly immaterial, but only the abstract likenesses thereof. Hence the Commentator says (De Anima iii) that the proposition quoted is true only of separate substances; because in a sense it is verified in their regard, and not in regard of other substances, as already stated.

Articulus 1

Argumentum 1

Ad primum sic proceditur. Videtur quod anima intellectiva seipsam cognoscat per suam essentiam.

Dicit enim Augustinus, IX de Trin., quod mens seipsam novit per seipsam, quoniam est incorporea.

Argumentum 2

Praeterea, Angelus et anima humana conveniunt in genere intellectualis substantiae. Sed Angelus intelligit seipsum per essentiam suam. Ergo et anima humana.

Argumentum 3

Praeterea, in his quae sunt sine materia, idem est intellectus et quod intelligitur, ut dicitur III de anima.

Sed mens humana est sine materia, non enim est actus corporis alicuius, ut supra dictum est.

Ergo in mente humana est idem intellectus et quod intelligitur.

Ergo intelligit se per essentiam suam.

Sed Contra

Sed contra est quod dicitur in III de anima, quod intellectus intelligit seipsum sicut et alia.

Sed alia non intelligit per essentias eorum, sed per eorum similitudines. Ergo neque se intelligit per essentiam suam.

Corpus

Respondeo dicendum quod unumquodque cognoscibile est secundum quod est in actu, et non secundum quod est in potentia, ut dicitur in IX metaphys., sic enim aliquid est ens et verum, quod sub cognitione cadit, prout actu est. Et hoc quidem manifeste apparet in rebus sensibilibus, non enim visus percipit coloratum in potentia, sed solum coloratum in actu. Et similiter intellectus manifestum est quod, inquantum est cognoscitivus rerum materialium, non cognoscit nisi quod est actu, et inde est quod non cognoscit materiam primam nisi secundum proportionem ad formam, ut dicitur in I physic..

Unde et in substantiis immaterialibus, secundum quod unaquaeque earum se habet ad hoc quod sit in actu per essentiam suam, ita se habet ad hoc quod sit per suam essentiam intelligibilis. Essentia igitur dei, quae est actus purus et perfectus, est simpliciter et perfecte secundum seipsam intelligibilis. Unde deus per suam essentiam non solum seipsum, sed etiam omnia intelligit. Angeli autem essentia est quidem in genere intelligibilium ut actus, non tamen ut actus purus neque completus. Unde eius intelligere non completur per essentiam suam, etsi enim per essentiam suam se intelligat Angelus, tamen non omnia potest per essentiam suam cognoscere, sed cognoscit alia a se per eorum similitudines.

Intellectus autem humanus se habet in genere rerum intelligibilium ut ens in potentia tantum, sicut et materia prima se habet in genere rerum sensibilium, unde possibilis nominatur. Sic igitur in sua essentia consideratus, se habet ut potentia intelligens. Unde ex seipso habet virtutem ut intelligat, non autem ut intelligatur, nisi secundum id quod fit actu.

Sic enim etiam Platonici posuerunt ordinem entium intelligibilium supra ordinem intellectuum, quia intellectus non intelligit nisi per participationem intelligibilis; participans autem est infra participatum, secundum eos. Si igitur intellectus humanus fieret actu per participationem formarum intelligibilium separatarum, ut Platonici posuerunt per huiusmodi participationem rerum incorporearum intellectus humanus seipsum intelligeret.

Sed quia connaturale est intellectui nostro, secundum statum praesentis vitae, quod ad materialia et sensibilia respiciat, sicut supra dictum est; consequens est ut sic seipsum intelligat intellectus noster, secundum quod fit actu per species a sensibilibus abstractas per lumen intellectus agentis, quod est actus ipsorum intelligibilium, et eis mediantibus intellectus possibilis. Non ergo per essentiam suam, sed per actum suum se cognoscit intellectus noster. Et hoc dupliciter. Uno quidem modo, particulariter, secundum quod socrates vel Plato percipit se habere animam intellectivam, ex hoc quod percipit se intelligere. Alio modo, in universali, secundum quod naturam humanae mentis ex actu intellectus consideramus. Sed verum est quod iudicium et efficacia huius cognitionis per quam naturam animae cognoscimus, competit nobis secundum derivationem luminis intellectus nostri a veritate divina, in qua rationes omnium rerum continentur, sicut supra dictum est.

Unde et Augustinus dicit, in IX de Trin., intuemur inviolabilem veritatem, ex qua perfecte, quantum possumus, definimus non qualis sit uniuscuiusque hominis mens, sed qualis esse sempiternis rationibus debeat.

Est autem differentia inter has duas cognitiones. Nam ad primam cognitionem de mente habendam, sufficit ipsa mentis praesentia, quae est principium actus ex quo mens percipit seipsam. Et ideo dicitur se cognoscere per suam praesentiam.

Sed ad secundam cognitionem de mente habendam, non sufficit eius praesentia, sed requiritur diligens et subtilis inquisitio.

Unde et multi naturam animae ignorant, et multi etiam circa naturam animae erraverunt. Propter quod Augustinus dicit, X de Trin., de tali inquisitione mentis, non velut absentem se quaerat mens cernere; sed praesentem quaerat discernere, idest cognoscere differentiam suam ab aliis rebus, quod est cognoscere quidditatem et naturam suam.

Ad 1

Ad primum ergo dicendum quod mens seipsam per seipsam novit, quia tandem in sui ipsius cognitionem pervenit, licet per suum actum, ipsa enim est quae cognoscitur, quia ipsa seipsam amat, ut ibidem subditur.

Potest enim aliquid dici per se notum dupliciter, vel quia per nihil aliud in eius notitiam devenitur, sicut dicuntur prima principia per se nota; vel quia non sunt cognoscibilia per accidens, sicut color est per se visibilis, substantia autem per accidens.

Ad 2

Ad secundum dicendum quod essentia Angeli est sicut actus in genere intelligibilium, et ideo se habet et ut intellectus, et ut intellectum. Unde Angelus suam essentiam per seipsum apprehendit. Non autem intellectus humanus, qui vel est omnino in potentia respectu intelligibilium, sicut intellectus possibilis; vel est actus intelligibilium quae abstrahuntur a phantasmatibus, sicut intellectus agens.

Ad 3

Ad tertium dicendum quod verbum illud philosophi universaliter verum est in omni intellectu. Sicut enim sensus in actu est sensibile, propter similitudinem sensibilis, quae est forma sensus in actu; ita intellectus in actu est intellectum in actu, propter similitudinem rei intellectae, quae est forma intellectus in actu. Et ideo intellectus humanus, qui fit in actu per speciem rei intellectae, per eandem speciem intelligitur, sicut per formam suam. Idem autem est dicere quod in his quae sunt sine materia, idem est intellectus et quod intelligitur, ac si diceretur quod in his quae sunt intellecta in actu, idem est intellectus et quod intelligitur, per hoc enim aliquid est intellectum in actu, quod est sine materia. Sed in hoc est differentia, quia quorundam essentiae sunt sine materia, sicut substantiae separatae quas Angelos dicimus, quarum unaquaeque et est intellecta et est intelligens, sed quaedam res sunt quarum essentiae non sunt sine materia, sed solum similitudines ab eis abstractae.

Unde et Commentator dicit, in III de anima, quod propositio inducta non habet veritatem nisi in substantiis separatis, verificatur enim quodammodo in eis quod non verificatur in aliis, ut dictum est.