Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that intellectual knowledge is not derived from sensible things. For Augustine says (Questions. 83, qu. 9) that "we cannot expect to learn the fulness of truth from the senses of the body." This he proves in two ways. First, because "whatever the bodily senses reach, is continually being changed; and what is never the same cannot be perceived." Secondly, because, "whatever we perceive by the body, even when not present to the senses, may be present to the imagination, as when we are asleep or angry: yet we cannot discern by the senses, whether what we perceive be the sensible object or the deceptive image thereof. Now nothing can be perceived which cannot be distinguished from its counterfeit." And so he concludes that we cannot expect to learn the truth from the senses. But intellectual knowledge apprehends the truth. Therefore intellectual knowledge cannot be conveyed by the senses.

Objection 2: Further, Augustine says (Gen. ad lit. xii, 16): "We must not thing that the body can make any impression on the spirit, as though the spirit were to supply the place of matter in regard to the body's action; for that which acts is in every way more excellent than that which it acts on." Whence he concludes that "the body does not cause its image in the spirit, but the spirit causes it in itself." Therefore intellectual knowledge is not derived from sensible things.

Objection 3: Further, an effect does not surpass the power of its cause. But intellectual knowledge extends beyond sensible things: for we understand some things which cannot be perceived by the senses. Therefore intellectual knowledge is not derived from sensible things.

On the contrary, The Philosopher says (Metaph. i, 1; Poster. ii, 15) that the principle of knowledge is in the senses.

I answer that, On this point the philosophers held three opinions. For Democritus held that "all knowledge is caused by images issuing from the bodies we think of and entering into our souls," as Augustine says in his letter to Dioscorus (cxviii, 4). And Aristotle says (De Somn. et Vigil.) that Democritus held that knowledge is cause by a "discharge of images." And the reason for this opinion was that both Democritus and the other early philosophers did not distinguish between intellect and sense, as Aristotle relates (De Anima iii, 3). Consequently, since the sense is affected by the sensible, they thought that all our knowledge is affected by this mere impression brought about by sensible things. Which impression Democritus held to be caused by a discharge of images.

Plato, on the other hand, held that the intellect is distinct from the senses: and that it is an immaterial power not making use of a corporeal organ for its action. And since the incorporeal cannot be affected by the corporeal, he held that intellectual knowledge is not brought about by sensible things affecting the intellect, but by separate intelligible forms being participated by the intellect, as we have said above (Articles 4,5). Moreover he held that sense is a power operating of itself. Consequently neither is sense, since it is a spiritual power, affected by the sensible: but the sensible organs are affected by the sensible, the result being that the soul is in a way roused to form within itself the species of the sensible. Augustine seems to touch on this opinion (Gen. ad lit. xii, 24) where he says that the "body feels not, but the soul through the body, which it makes use of as a kind of messenger, for reproducing within itself what is announced from without." Thus according to Plato, neither does intellectual knowledge proceed from sensible knowledge, nor sensible knowledge exclusively from sensible things; but these rouse the sensible soul to the sentient act, while the senses rouse the intellect to the act of understanding.

Aristotle chose a middle course. For with Plato he agreed that intellect and sense are different. But he held that the sense has not its proper operation without the cooperation of the body; so that to feel is not an act of the soul alone, but of the "composite." And he held the same in regard to all the operations of the sensitive part. Since, therefore, it is not unreasonable that the sensible objects which are outside the soul should produce some effect in the "composite," Aristotle agreed with Democritus in this, that the operations of the sensitive part are caused by the impression of the sensible on the sense: not by a discharge, as Democritus said, but by some kind of operation. For Democritus maintained that every operation is by way of a discharge of atoms, as we gather from De Gener. i, 8. But Aristotle held that the intellect has an operation which is independent of the body's cooperation. Now nothing corporeal can make an impression on the incorporeal. And therefore in order to cause the intellectual operation according to Aristotle, the impression caused by the sensible does not suffice, but something more noble is required, for "the agent is more noble than the patient," as he says (De Gener. i, 5). Not, indeed, in the sense that the intellectual operation is effected in us by the mere intellectual operation is effected in us by the mere impression of some superior beings, as Plato held; but that the higher and more noble agent which he calls the active intellect, of which we have spoken above (Question 79, Articles 3,4) causes the phantasms received from the senses to be actually intelligible, by a process of abstraction.

According to this opinion, then, on the part of the phantasms, intellectual knowledge is caused by the senses. But since the phantasms cannot of themselves affect the passive intellect, and require to be made actually intelligible by the active intellect, it cannot be said that sensible knowledge is the total and perfect cause of intellectual knowledge, but rather that it is in a way the material cause.

Reply to Objection 1: Those words of Augustine mean that we must not expect the entire truth from the senses. For the light of the active intellect is needed, through which we achieve the unchangeable truth of changeable things, and discern things themselves from their likeness.

Reply to Objection 2: In this passage Augustine speaks not of intellectual but of imaginary knowledge. And since, according to the opinion of Plato, the imagination has an operation which belongs to the soul only, Augustine, in order to show that corporeal images are impressed on the imagination, not by bodies but by the soul, uses the same argument as Aristotle does in proving that the active intellect must be separate, namely, because "the agent is more noble than the patient." And without doubt, according to the above opinion, in the imagination there must needs be not only a passive but also an active power. But if we hold, according to the opinion of Aristotle, that the action of the imagination, is an action of the "composite," there is no difficulty; because the sensible body is more noble than the organ of the animal, in so far as it is compared to it as a being in act to a being in potentiality; even as the object actually colored is compared to the pupil which is potentially colored. It may, however, be said, although the first impression of the imagination is through the agency of the sensible, since "fancy is movement produced in accordance with sensation" (De Anima iii, 3), that nevertheless there is in man an operation which by synthesis and analysis forms images of various things, even of things not perceived by the senses. And Augustine's words may be taken in this sense.

Reply to Objection 3: Sensitive knowledge is not the entire cause of intellectual knowledge. And therefore it is not strange that intellectual knowledge should extend further than sensitive knowledge.

Articulus 6

Argumentum 1

Ad sextum sic proceditur. Videtur quod intellectiva cognitio non accipiatur a rebus sensibilibus.

Dicit enim Augustinus, in libro octoginta trium quaest., quod non est expectanda sinceritas veritatis a corporis sensibus.

Et hoc probat dupliciter. Uno modo, per hoc quod omne quod corporeus sensus attingit, sine ulla intermissione temporis commutatur, quod autem non manet, percipi non potest.

Alio modo, per hoc quod omnia quae per corpus sentimus, etiam cum non adsunt sensibus, imagines tamen eorum patimur, ut in somno vel furore; non autem sensibus discernere valemus utrum ipsa sensibilia, vel imagines eorum falsas sentiamus.

Nihil autem percipi potest quod a falso non discernitur.

Et sic concludit quod non est expectanda veritas a sensibus.

Sed cognitio intellectualis est apprehensiva veritatis.

Non ergo cognitio intellectualis est expectanda a sensibus.

Argumentum 2

Praeterea, Augustinus dicit, XII super Gen. Ad litt., non est putandum facere aliquid corpus in spiritum, tanquam spiritus corpori facienti materiae vice subdatur, omni enim modo praestantior est qui facit, ea re de qua aliquid facit.

Unde concludit quod imaginem corporis non corpus in spiritu, sed ipse spiritus in seipso facit.

Non ergo intellectualis cognitio a sensibilibus derivatur.

Argumentum 3

Praeterea, effectus non se extendit ultra virtutem suae causae.

Sed intellectualis cognitio se extendit ultra sensibilia, intelligimus enim quaedam quae sensu percipi non possunt.

Intellectualis ergo cognitio non derivatur a rebus sensibilibus.

Sed Contra

Sed contra est quod philosophus probat, I metaphys., et in fine poster., quod principium nostrae cognitionis est a sensu.

Corpus

Respondeo dicendum quod circa istam quaestionem triplex fuit philosophorum opinio.

Democritus enim posuit quod nulla est alia causa cuiuslibet nostrae cognitionis, nisi cum ab his corporibus quae cogitamus, veniunt atque intrant imagines in animas nostras; ut Augustinus dicit in epistola sua ad dioscorum.

Et Aristoteles etiam dicit, in libro de somn. Et vigil., quod democritus posuit cognitionem fieri per idola et defluxiones.

Et huius positionis ratio fuit, quia tam ipse democritus quam alii antiqui naturales non ponebant intellectum differre a sensu, ut Aristoteles dicit in libro de anima.

Et ideo, quia sensus immutatur a sensibili, arbitrabantur omnem nostram cognitionem fieri per solam immutationem a sensibilibus. Quam quidem immutationem democritus asserebat fieri per imaginum defluxiones.

Plato vero e contrario posuit intellectum differre a sensu; et intellectum quidem esse virtutem immaterialem organo corporeo non utentem in suo actu. Et quia incorporeum non potest immutari a corporeo, posuit quod cognitio intellectualis non fit per immutationem intellectus a sensibilibus, sed per participationem formarum intelligibilium separatarum, ut dictum est. Sensum etiam posuit virtutem quandam per se operantem. Unde nec ipse sensus, cum sit quaedam vis spiritualis, immutatur a sensibilibus, sed organa sensuum a sensibilibus immutantur, ex qua immutatione anima quodammodo excitatur ut in se species sensibilium formet. Et hanc opinionem tangere videtur Augustinus, XII super Gen. Ad litt., ubi dicit quod corpus non sentit, sed anima per corpus, quo velut nuntio utitur ad formandum in seipsa quod extrinsecus nuntiatur.

Sic igitur secundum Platonis opinionem, neque intellectualis cognitio a sensibili procedit, neque etiam sensibilis totaliter a sensibilibus rebus; sed sensibilia excitant animam sensibilem ad sentiendum, et similiter sensus excitant animam intellectivam ad intelligendum.

Aristoteles autem media via processit. Posuit enim cum Platone intellectum differre a sensu. Sed sensum posuit propriam operationem non habere sine communicatione corporis; ita quod sentire non sit actus animae tantum, sed coniuncti.

Et similiter posuit de omnibus operationibus sensitivae partis.

Quia igitur non est inconveniens quod sensibilia quae sunt extra animam, causent aliquid in coniunctum, in hoc Aristoteles cum democrito concordavit, quod operationes sensitivae partis causentur per impressionem sensibilium in sensum, non per modum defluxionis, ut democritus posuit, sed per quandam operationem. Nam et democritus omnem actionem fieri posuit per influxionem atomorum, ut patet in I de generat.. Intellectum vero posuit Aristoteles habere operationem absque communicatione corporis.

Nihil autem corporeum imprimere potest in rem incorpoream.

Et ideo ad causandam intellectualem operationem, secundum Aristotelem, non sufficit sola impressio sensibilium corporum, sed requiritur aliquid nobilius, quia agens est honorabilius patiente, ut ipse dicit. Non tamen ita quod intellectualis operatio causetur in nobis ex sola impressione aliquarum rerum superiorum, ut Plato posuit, sed illud superius et nobilius agens quod vocat intellectum agentem, de quo iam supra diximus, facit phantasmata a sensibus accepta intelligibilia in actu, per modum abstractionis cuiusdam.

Secundum hoc ergo, ex parte phantasmatum intellectualis operatio a sensu causatur. Sed quia phantasmata non sufficiunt immutare intellectum possibilem, sed oportet quod fiant intelligibilia actu per intellectum agentem; non potest dici quod sensibilis cognitio sit totalis et perfecta causa intellectualis cognitionis, sed magis quodammodo est materia causae.

Ad 1

Ad primum ergo dicendum quod per verba illa Augustini datur intelligi quod veritas non sit totaliter a sensibus expectanda. Requiritur enim lumen intellectus agentis, per quod immutabiliter veritatem in rebus mutabilibus cognoscamus, et discernamus ipsas res a similitudinibus rerum.

Ad 2

Ad secundum dicendum quod Augustinus ibi non loquitur de intellectuali cognitione, sed de imaginaria. Et quia, secundum Platonis opinionem, vis imaginaria habet operationem quae est animae solius; eadem ratione usus est Augustinus ad ostendendum quod corpora non imprimunt suas similitudines in vim imaginariam, sed hoc facit ipsa anima, qua utitur Aristoteles ad probandum intellectum agentem esse aliquid separatum, quia scilicet agens est honorabilius patiente. Et procul dubio oportet, secundum hanc positionem, in VI imaginativa ponere non solum potentiam passivam, sed etiam activam.

Sed si ponamus, secundum opinionem Aristotelis, quod actio virtutis imaginativae sit coniuncti, nulla sequitur difficultas, quia corpus sensibile est nobilius organo animalis, secundum hoc quod comparatur ad ipsum ut ens in actu ad ens in potentia, sicut coloratum in actu ad pupillam, quae colorata est in potentia. Posset tamen dici quod, quamvis prima immutatio virtutis imaginariae sit per motum sensibilium, quia phantasia est motus factus secundum sensum, ut dicitur in libro de anima; tamen est quaedam operatio animae in homine quae dividendo et componendo format diversas rerum imagines, etiam quae non sunt a sensibus acceptae.

Et quantum ad hoc possunt accipi verba Augustini.

Ad 3

Ad tertium dicendum quod sensitiva cognitio non est tota causa intellectualis cognitionis. Et ideo non est mirum si intellectualis cognitio ultra sensitivam se extendit.