Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the intelligible species are derived by the soul from some separate forms. For whatever is such by participation is caused by what is such essentially; for instance, that which is on fire is reduced to fire as the cause thereof. But the intellectual soul forasmuch as it is actually understanding, participates the thing understood: for, in a way, the intellect in act is the thing understood in act. Therefore what in itself and in its essence is understood in act, is the cause that the intellectual soul actually understands. Now that which in its essence is actually understood is a form existing without matter. Therefore the intelligible species, by which the soul understands, are caused by some separate forms.

Objection 2: Further, the intelligible is to the intellect, as the sensible is to the sense. But the sensible species which are in the senses, and by which we sense, are caused by the sensible object which exists actually outside the soul. Therefore the intelligible species, by which our intellect understands, are caused by some things actually intelligible, existing outside the soul. But these can be nothing else than forms separate from matter. Therefore the intelligible forms of our intellect are derived from some separate substances.

Objection 3: Further, whatever is in potentiality is reduced to act by something actual. If, therefore, our intellect, previously in potentiality, afterwards actually understands, this must needs be caused by some intellect which is always in act. But this is a separate intellect. Therefore the intelligible species, by which we actually understand, are caused by some separate substances.

On the contrary, If this were true we should not need the senses in order to understand. And this is proved to be false especially from the fact that if a man be wanting in a sense, he cannot have any knowledge of the sensibles corresponding to that sense.

I answer that, Some have held that the intelligible species of our intellect are derived from certain separate forms or substances. And this in two ways. For Plato, as we have said (Article 1), held that the forms of sensible things subsist by themselves without matter; for instance, the form of a man which he called "per se" man, and the form or idea of a horse which is called "per se" horse, and so forth. He said therefore that these forms are participated both by our soul and by corporeal matter; by our soul, to the effect of knowledge thereof, and by corporeal matter to the effect of existence: so that, just as corporeal matter by participating the idea of a stone, becomes an individuating stone, so our intellect, by participating the idea of a stone, is made to understand a stone. Now participation of an idea takes place by some image of the idea in the participator, just as a model is participated by a copy. So just as he held that the sensible forms, which are in corporeal matter, are derived from the ideas as certain images thereof: so he held that the intelligible species of our intellect are images of the ideas, derived therefrom. And for this reason, as we have said above (Article 1), he referred sciences and definitions to those ideas.

But since it is contrary to the nature of sensible things that their forms should subsist without matter, as Aristotle proves in many ways (Metaph. vi), Avicenna (De Anima v) setting this opinion aside, held that the intelligible species of all sensible things, instead of subsisting in themselves without matter, pre-exist immaterially in the separate intellects: from the first of which, said he, such species are derived by a second, and so on to the last separate intellect which he called the "active intelligence," from which, according to him, intelligible species flow into our souls, and sensible species into corporeal matter. And so Avicenna agrees with Plato in this, that the intelligible species of our intellect are derived from certain separate forms; but these Plato held to subsist of themselves, while Avicenna placed them in the "active intelligence." They differ, too, in this respect, that Avicenna held that the intelligible species do not remain in our intellect after it has ceased actually to understand, and that it needs to turn (to the active intellect) in order to receive them anew. Consequently he does not hold that the soul has innate knowledge, as Plato, who held that the participated ideas remain immovably in the soul.

But in this opinion no sufficient reason can be assigned for the soul being united to the body. For it cannot be said that the intellectual soul is united to the body for the sake of the body: for neither is form for the sake of matter, nor is the mover for the sake of the moved, but rather the reverse. Especially does the body seem necessary to the intellectual soul, for the latter's proper operation which is to understand: since as to its being the soul does not depend on the body. But if the soul by its very nature had an inborn aptitude for receiving intelligible species through the influence of only certain separate principles, and were not to receive them from the senses, it would not need the body in order to understand: wherefore to no purpose would it be united to the body.

But if it be said that our soul needs the senses in order to understand, through being in some way awakened by them to the consideration of those things, the intelligible species of which it receives from the separate principles: even this seems an insufficient explanation. For this awakening does not seem necessary to the soul, except in as far as it is overcome by sluggishness, as the Platonists expressed it, and by forgetfulness, through its union with the body: and thus the senses would be of no use to the intellectual soul except for the purpose of removing the obstacle which the soul encounters through its union with the body. Consequently the reason of the union of the soul with the body still remains to be sought.

And if it be said with Avicenna, that the senses are necessary to the soul, because by them it is aroused to turn to the "active intelligence" from which it receives the species: neither is this a sufficient explanation. Because if it is natural for the soul to understand through species derived from the "active intelligence," it follows that at times the soul of an individual wanting in one of the senses can turn to the active intelligence, either from the inclination of its very nature, or through being roused by another sense, to the effect of receiving the intelligible species of which the corresponding sensible species are wanting. And thus a man born blind could have knowledge of colors; which is clearly untrue. We must therefore conclude that the intelligible species, by which our soul understands, are not derived from separate forms.

Reply to Objection 1: The intelligible species which are participated by our intellect are reduced, as to their first cause, to a first principle which is by its essence intelligible---namely, God. But they proceed from that principle by means of the sensible forms and material things, from which we gather knowledge, as Dionysius says (Div. Nom. vii).

Reply to Objection 2: Material things, as to the being which they have outside the soul, may be actually sensible, but not actually intelligible. Wherefore there is no comparison between sense and intellect.

Reply to Objection 3: Our passive intellect is reduced from potentiality to act by some being in act, that is, by the active intellect, which is a power of the soul, as we have said (Question 79, Article 4); and not by a separate intelligence, as proximate cause, although perchance as remote cause.

Articulus 4

Argumentum 1

Ad quartum sic proceditur. Videtur quod species intelligibiles effluant in animam ab aliquibus formis separatis. Omne enim quod per participationem est tale, causatur ab eo quod est per essentiam tale; sicut quod est ignitum reducitur sicut in causam in ignem. Sed anima intellectiva, secundum quod est actu intelligens, participat ipsa intelligibilia, intellectus enim in actu, quodammodo est intellectum in actu. Ergo ea quae secundum se et per essentiam suam sunt intellecta in actu, sunt causae animae intellectivae quod actu intelligat. Intellecta autem in actu per essentiam suam, sunt formae sine materia existentes.

Species igitur intelligibiles quibus anima intelligit, causantur a formis aliquibus separatis.

Argumentum 2

Praeterea, intelligibilia se habent ad intellectum, sicut sensibilia ad sensum. Sed sensibilia quae sunt in actu extra animam, sunt causae specierum sensibilium quae sunt in sensu, quibus sentimus. Ergo species intelligibiles quibus intellectus noster intelligit, causantur ab aliquibus actu intelligibilibus extra animam existentibus. Huiusmodi autem non sunt nisi formae a materia separatae. Formae igitur intelligibiles intellectus nostri effluunt ab aliquibus substantiis separatis.

Argumentum 3

Praeterea, omne quod est in potentia, reducitur in actum per id quod est actu. Si ergo intellectus noster, prius in potentia existens, postmodum actu intelligat, oportet quod hoc causetur ab aliquo intellectu qui semper est in actu. Hic autem est intellectus separatus. Ergo ab aliquibus substantiis separatis causantur species intelligibiles quibus actu intelligimus.

Sed Contra

Sed contra est quia secundum hoc sensibus non indigeremus ad intelligendum. Quod patet esse falsum ex hoc praecipue quod qui caret uno sensu, nullo modo potest habere scientiam de sensibilibus illius sensus.

Corpus

Respondeo dicendum quod quidam posuerunt species intelligibiles nostri intellectus procedere ab aliquibus formis vel substantiis separatis. Et hoc dupliciter.

Plato enim, sicut dictum est, posuit formas rerum sensibilium per se sine materia subsistentes; sicut formam hominis, quam nominabat per se hominem, et formam vel ideam equi, quam nominabat per se equum, et sic de aliis. Has ergo formas separatas ponebat participari et ab anima nostra, et a materia corporali; ab anima quidem nostra ad cognoscendum, a materia vero corporali ad essendum; ut sicut materia corporalis per hoc quod participat ideam lapidis, fit hic lapis, ita intellectus noster per hoc quod participat ideam lapidis, fit intelligens lapidem. Participatio autem ideae fit per aliquam similitudinem ipsius ideae in participante ipsam, per modum quo exemplar participatur ab exemplato. Sicut igitur ponebat formas sensibiles quae sunt in materia corporali, effluere ab ideis sicut quasdam earum similitudines; ita ponebat species intelligibiles nostri intellectus esse similitudines quasdam idearum ab eis effluentes. Et propter hoc, ut supra dictum est, scientias et definitiones ad ideas referebat.

Sed quia contra rationem rerum sensibilium est quod earum formae subsistant absque materiis, ut Aristoteles multipliciter probat; ideo Avicenna, hac positione remota, posuit omnium rerum sensibilium intelligibiles species, non quidem per se subsistere absque materia, sed praeexistere immaterialiter in intellectibus separatis; a quorum primo derivantur huiusmodi species in sequentem, et sic de aliis usque ad ultimum intellectum separatum, quem nominat intellectum agentem; a quo, ut ipse dicit, effluunt species intelligibiles in animas nostras, et formae sensibiles in materiam corporalem. Et sic in hoc Avicenna cum Platone concordat, quod species intelligibiles nostri intellectus effluunt a quibusdam formis separatis, quas tamen Plato dicit per se subsistere, Avicenna vero ponit eas in intelligentia agente. Differunt etiam quantum ad hoc, quod Avicenna ponit species intelligibiles non remanere in intellectu nostro postquam desinit actu intelligere; sed indiget ut iterato se convertat ad recipiendum de novo. Unde non ponit scientiam animae naturaliter inditam, sicut Plato, qui ponit participationes idearum immobiliter in anima permanere.

Sed secundum hanc positionem sufficiens ratio assignari non posset quare anima nostra corpori uniretur. Non enim potest dici quod anima intellectiva corpori uniatur propter corpus, quia nec forma est propter materiam, nec motor propter mobile, sed potius e converso. Maxime autem videtur corpus esse necessarium animae intellectivae ad eius propriam operationem, quae est intelligere, quia secundum esse suum a corpore non dependet.

Si autem anima species intelligibiles secundum suam naturam apta nata esset recipere per influentiam aliquorum separatorum principiorum tantum, et non acciperet eas ex sensibus, non indigeret corpore ad intelligendum, unde frustra corpori uniretur.

Si autem dicatur quod indiget anima nostra sensibus ad intelligendum, quibus quodammodo excitetur ad consideranda ea quorum species intelligibiles a principiis separatis recipit; hoc non videtur sufficere. Quia huiusmodi excitatio non videtur necessaria animae nisi inquantum est consopita, secundum Platonicos, quodammodo et obliviosa propter unionem ad corpus, et sic sensus non proficerent animae intellectivae nisi ad tollendum impedimentum quod animae provenit ex corporis unione. Remanet igitur quaerendum quae sit causa unionis animae ad corpus.

Si autem dicatur, secundum Avicennam, quod sensus sunt animae necessarii, quia per eos excitatur ut convertat se ad intelligentiam agentem, a qua recipit species; hoc quidem non sufficit. Quia si in natura animae est ut intelligat per species ab intelligentia agente effluxas, sequeretur quod quandoque anima possit se convertere ad intelligentiam agentem ex inclinatione suae naturae, vel etiam excitata per alium sensum, ut convertat se ad intelligentiam agentem ad recipiendum species sensibilium quorum sensum aliquis non habet. Et sic caecus natus posset habere scientiam de coloribus, quod est manifeste falsum. Unde dicendum est quod species intelligibiles quibus anima nostra intelligit, non effluunt a formis separatis.

Ad 1

Ad primum ergo dicendum quod species intelligibiles quas participat noster intellectus, reducuntur sicut in primam causam in aliquod principium per suam essentiam intelligibile, scilicet in deum. Sed ab illo principio procedunt mediantibus formis rerum sensibilium et materialium, a quibus scientiam colligimus, ut dionysius dicit.

Ad 2

Ad secundum dicendum quod res materiales, secundum esse quod habent extra animam, possunt esse sensibiles actu; non autem actu intelligibiles. Unde non est simile de sensu et intellectu.

Ad 3

Ad tertium dicendum quod intellectus noster possibilis reducitur de potentia ad actum per aliquod ens actu, idest per intellectum agentem, qui est virtus quaedam animae nostrae, ut dictum est, non autem per aliquem intellectum separatum, sicut per causam proximam; sed forte sicut per causam remotam.