Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the human soul in the present state of life can understand immaterial substances in themselves. For Augustine (De Trin. ix, 3) says: "As the mind itself acquires the knowledge of corporeal things by means of the corporeal senses, so it gains from itself the knowledge of incorporeal things." But these are the immaterial substances. Therefore the human mind understands immaterial substances.

Objection 2: Further, like is known by like. But the human mind is more akin to immaterial than to material things; since its own nature is immaterial, as is clear from what we have said above (Question 76, Article 1). Since then our mind understands material things, much more is it able to understand immaterial things.

Objection 3: Further, the fact that objects which are in themselves most sensible are not most felt by us, comes from sense being corrupted by their very excellence. But the intellect is not subject to such a corrupting influence from its object, as is stated De Anima iii, 4. Therefore things which are in themselves in the highest degree of intelligibility, are likewise to us most intelligible. As material things, however, are intelligible only so far as we make them actually so by abstracting them from material conditions, it is clear that those substances are more intelligible in themselves whose nature is immaterial. Therefore they are much more known to us than are material things.

Objection 4: Further, the Commentator says (Metaph. ii) that "nature would be frustrated in its end" were we unable to understand abstract substances, "because it would have made what in itself is naturally intelligible not to be understood at all." But in nature nothing is idle or purposeless. Therefore immaterial substances can be understood by us.

Objection 5: Further, as sense is to the sensible, so is intellect to the intelligible. But our sight can see all things corporeal, whether superior and incorruptible; or lower and corruptible. Therefore our intellect can understand all intelligible substances, even the superior and immaterial.

On the contrary, It is written (Wis. 9:16): "The things that are in heaven, who shall search out?" But these substances are said to be in heaven, according to Mt. 18:10, "Their angels in heaven," etc. Therefore immaterial substances cannot be known by human investigation.

I answer that, In the opinion of Plato, immaterial substances are not only understood by us, but are the objects we understand first of all. For Plato taught that immaterial subsisting forms, which he called "Ideas," are the proper objects of our intellect, and thus first and "per se" understood by us; and, further, that material objects are known by the soul inasmuch as phantasy and sense are mixed up with the mind. Hence the purer the intellect is, so much the more clearly does it perceive the intelligible truth of immaterial things.

But in Aristotle's opinion, which experience corroborates, our intellect in its present state of life has a natural relationship to the natures of material things; and therefore it can only understand by turning to the phantasms, as we have said above (Question 84, Article 7). Thus it clearly appears that immaterial substances which do not fall under sense and imagination, cannot first and "per se" be known by us, according to the mode of knowledge which experience proves us to have.

Nevertheless Averroes (Comment. De Anima iii) teaches that in this present life man can in the end arrive at the knowledge of separate substances by being coupled or united to some separate substance, which he calls the "active intellect," and which, being a separate substance itself, can naturally understand separate substances. Hence, when it is perfectly united to us so that by its means we are able to understand perfectly, we also shall be able to understand separate substances, as in the present life through the medium of the passive intellect united to us, we can understand material things. Now he said that the active intellect is united to us, thus. For since we understand by means of both the active intellect and intelligible objects, as, for instance, we understand conclusions by principles understood; it is clear that the active intellect must be compared to the objects understood, either as the principal agent is to the instrument, or as form to matter. For an action is ascribed to two principles in one of these two ways; to a principal agent and to an instrument, as cutting to the workman and the saw; to a form and its subject, as heating to heat and fire. In both these ways the active intellect can be compared to the intelligible object as perfection is to the perfectible, and as act is to potentiality. Now a subject is made perfect and receives its perfection at one and the same time, as the reception of what is actually visible synchronizes with the reception of light in the eye. Therefore the passive intellect receives the intelligible object and the active intellect together; and the more numerous the intelligible objects received, so much the nearer do we come to the point of perfect union between ourselves and the active intellect; so much so that when we understand all the intelligible objects, the active intellect becomes one with us, and by its instrumentality we can understand all things material and immaterial. In this he makes the ultimate happiness of man to consist. Nor, as regards the present inquiry, does it matter whether the passive intellect in that state of happiness understands separate substances by the instrumentality of the active intellect, as he himself maintains, or whether (as he says Alexander holds) the passive intellect can never understand separate substances (because according to him it is corruptible), but man understands separate substances by means of the active intellect.

This opinion, however, is untrue. First, because, supposing the active intellect to be a separate substance, we could not formally understand by its instrumentality, for the medium of an agent's formal action consists in its form and act, since every agent acts according to its actuality, as was said of the passive intellect (Question 70, Article 1). Secondly, this opinion is untrue, because in the above explanation, the active intellect, supposing it to be a separate substance, would not be joined to us in its substance, but only in its light, as participated in things understood; and would not extend to the other acts of the active intellect so as to enable us to understand immaterial substances; just as when we see colors set off by the sun, we are not united to the substance of the sun so as to act like the sun, but its light only is united to us, that we may see the colors. Thirdly, this opinion is untrue, because granted that, as above explained, the active intellect were united to us in substance, still it is not said that it is wholly so united in regard to one intelligible object, or two; but rather in regard to all intelligible objects. But all such objects together do not equal the force of the active intellect, as it is a much greater thing to understand separate substances than to understand all material things. Hence it clearly follows that the knowledge of all material things would not make the active intellect to be so united to us as to enable us by its instrumentality to understand separate substances.

Fourthly, this opinion is untrue, because it is hardly possible for anyone in this world to understand all material things: and thus no one, or very few, could reach to perfect felicity; which is against what the Philosopher says (Ethic. i, 9), that happiness is a "kind of common good, communicable to all capable of virtue." Further, it is unreasonable that only the few of any species attain to the end of the species.

Fifthly, the Philosopher expressly says (Ethic. i, 10), that happiness is "an operation according to perfect virtue"; and after enumerating many virtues in the tenth book, he concludes (Ethic. i, 7) that ultimate happiness consisting in the knowledge of the highest things intelligible is attained through the virtue of wisdom, which in the sixth chapter he had named as the chief of speculative sciences. Hence Aristotle clearly places the ultimate felicity of man in the knowledge of separate substances, obtainable by speculative science; and not by being united to the active intellect as some imagined.

Sixthly, as was shown above (Question 79, Article 4), the active intellect is not a separate substance; but a faculty of the soul, extending itself actively to the same objects to which the passive intellect extends receptively; because, as is stated (De Anima iii, 5), the passive intellect is "all things potentially," and the active intellect is "all things in act." Therefore both intellects, according to the present state of life, extend to material things only, which are made actually intelligible by the active intellect, and are received in the passive intellect. Hence in the present state of life we cannot understand separate immaterial substances in themselves, either by the passive or by the active intellect.

Reply to Objection 1: Augustine may be taken to mean that the knowledge of incorporeal things in the mind can be gained by the mind itself. This is so true that philosophers also say that the knowledge concerning the soul is a principle for the knowledge of separate substances. For by knowing itself, it attains to some knowledge of incorporeal substances, such as is within its compass; not that the knowledge of itself gives it a perfect and absolute knowledge of them.

Reply to Objection 2: The likeness of nature is not a sufficient cause of knowledge; otherwise what Empedocles said would be true ---that the soul needs to have the nature of all in order to know all. But knowledge requires that the likeness of the thing known be in the knower, as a kind of form thereof. Now our passive intellect, in the present state of life, is such that it can be informed with similitudes abstracted from phantasms: and therefore it knows material things rather than immaterial substances.

Reply to Objection 3: There must needs be some proportion between the object and the faculty of knowledge; such as of the active to the passive, and of perfection to the perfectible. Hence that sensible objects of great power are not grasped by the senses, is due not merely to the fact that they corrupt the organ, but also to their being improportionate to the sensitive power. And thus it is that immaterial substances are improportionate to our intellect, in our present state of life, so that it cannot understand them.

Reply to Objection 4: This argument of the Commentator fails in several ways. First, because if separate substances are not understood by us, it does not follow that they are not understood by any intellect; for they are understood by themselves, and by one another.

Secondly, to be understood by us is not the end of separate substances: while only that is vain and purposeless, which fails to attain its end. It does not follow, therefore, that immaterial substances are purposeless, even if they are not understood by us at all.

Reply to Objection 5: Sense knows bodies, whether superior or inferior, in the same way, that is, by the sensible acting on the organ. But we do not understand material and immaterial substances in the same way. The former we understand by a process of abstraction, which is impossible in the case of the latter, for there are no phantasms of what is immaterial.

Articulus 1

Argumentum 1

Ad primum sic proceditur. Videtur quod anima humana, secundum statum vitae praesentis, possit intelligere substantias immateriales per seipsas.

Dicit enim Augustinus, in IX de Trin., mens ipsa, sicut corporearum rerum notitias per sensus corporis colligit, sic incorporearum rerum per semetipsam.

Huiusmodi autem sunt substantiae immateriales.

Ergo mens substantias immateriales intelligit.

Argumentum 2

Praeterea, simile simili cognoscitur. Sed magis assimilatur mens humana rebus immaterialibus quam materialibus, cum ipsa mens sit immaterialis, ut ex supradictis patet.

Cum ergo mens nostra intelligat res materiales, multo magis intelligit res immateriales.

Argumentum 3

Praeterea, quod ea quae sunt secundum se maxime sensibilia, non maxime sentiantur a nobis, provenit ex hoc quod excellentiae sensibilium corrumpunt sensum. Sed excellentiae intelligibilium non corrumpunt intellectum, ut dicitur in III de anima.

Ergo ea quae sunt secundum se maxime intelligibilia, sunt etiam maxime intelligibilia nobis. Sed cum res materiales non sint intelligibiles nisi quia facimus eas intelligibiles actu, abstrahendo a materia; manifestum est quod magis sint secundum se intelligibiles substantiae quae secundum suam naturam sunt immateriales. Ergo multo magis intelliguntur a nobis quam res materiales.

Argumentum 4

Praeterea, Commentator dicit, in II metaphys., quod si substantiae abstractae non possent intelligi a nobis, tunc natura otiose egisset, quia fecit illud quod est naturaliter in se intellectum, non intellectum ab aliquo.

Sed nihil est otiosum sive frustra in natura.

Ergo substantiae immateriales possunt intelligi a nobis.

Argumentum 5

Praeterea, sicut se habet sensus ad sensibilia, ita se habet intellectus ad intelligibilia. Sed visus noster potest videre omnia corpora, sive sint superiora et incorruptibilia, sive sint inferiora et corruptibilia. Ergo intellectus noster potest intelligere omnes substantias intelligibiles, et superiores et immateriales.

Sed Contra

Sed contra est quod dicitur Sap. IX, quae in caelis sunt, quis investigabit? in caelis autem dicuntur huiusmodi substantiae esse; secundum illud Matth. XVIII, Angeli eorum in caelis etc..

Ergo non possunt substantiae immateriales per investigationem humanam cognosci.

Corpus

Respondeo dicendum quod secundum opinionem Platonis, substantiae immateriales non solum a nobis intelliguntur, sed etiam sunt prima a nobis intellecta.

Posuit enim Plato formas immateriales subsistentes, quas ideas vocabat, esse propria obiecta nostri intellectus, et ita primo et per se intelliguntur a nobis.

Applicatur tamen animae cognitio rebus materialibus, secundum quod intellectui permiscetur phantasia et sensus. Unde quanto magis intellectus fuerit depuratus, tanto magis percipit immaterialium intelligibilem veritatem.

Sed secundum Aristotelis sententiam, quam magis experimur, intellectus noster, secundum statum praesentis vitae, naturalem respectum habet ad naturas rerum materialium; unde nihil intelligit nisi convertendo se ad phantasmata, ut ex dictis patet.

Et sic manifestum est quod substantias immateriales, quae sub sensu et imaginatione non cadunt, primo et per se, secundum modum cognitionis nobis expertum, intelligere non possumus.

Sed tamen Averroes, in comment. Tertii de anima, ponit quod in fine in hac vita homo pervenire potest ad hoc quod intelligat substantias separatas, per continuationem vel unionem cuiusdam substantiae separatae nobis, quam vocat intellectum agentem, qui quidem, cum sit substantia separata, naturaliter substantias separatas intelligit. Unde cum fuerit nobis perfecte unitus, sic ut per eum perfecte intelligere possimus, intelligemus et nos substantias separatas; sicut nunc per intellectum possibilem nobis unitum intelligimus res materiales. Ponit autem intellectum agentem sic nobis uniri. Cum enim nos intelligamus per intellectum agentem et per intelligibilia speculata, ut patet cum conclusiones intelligimus per principia intellecta; necesse est quod intellectus agens comparetur ad intellecta speculata vel sicut agens principale ad instrumenta, vel sicut forma ad materiam. His enim duobus modis attribuitur actio aliqua duobus principiis, principali quidem agenti et instrumento, sicut sectio artifici et serrae; formae autem et subiecto, sicut calefactio calori et igni.

Sed utroque modo intellectus agens comparabitur ad intelligibilia speculata sicut perfectio ad perfectibile, et actus ad potentiam.

Simul autem recipitur in aliquo perfectum et perfectio; sicut visibile in actu et lumen in pupilla. Simul igitur in intellectu possibili recipiuntur intellecta speculata et intellectus agens.

Et quanto plura intellecta speculata recipimus, tanto magis appropinquamus ad hoc quod intellectus agens perfecte uniatur nobis. Ita quod cum omnia intellecta speculata cognoverimus, intellectus agens perfecte unietur nobis; et poterimus per eum omnia cognoscere materialia et immaterialia. Et in hoc ponit ultimam hominis felicitatem. Nec refert, quantum ad propositum pertinet, utrum in illo statu felicitatis intellectus possibilis intelligat substantias separatas per intellectum agentem, ut ipse sentit, vel, ut ipse imponit Alexandro, intellectus possibilis nunquam intelligat substantias separatas (propter hoc quod ponit intellectum possibilem corruptibilem), sed homo intelligat substantias separatas per intellectum agentem.

Sed praedicta stare non possunt. Primo quidem quia, si intellectus agens est substantia separata, impossibile est quod per ipsam formaliter intelligamus, quia id quo formaliter agens agit, est forma et actus agentis; cum omne agens agat inquantum est actu.

Sicut etiam supra dictum est circa intellectum possibilem.

Secundo quia, secundum modum praedictum, intellectus agens, si est substantia separata, non uniretur nobis secundum suam substantiam; sed solum lumen eius, secundum quod participatur in intellectis speculatis; et non quantum ad alias actiones intellectus agentis, ut possimus per hoc intelligere substantias immateriales. Sicut dum videmus colores illuminatos a sole, non unitur nobis substantia solis, ut possimus actiones solis agere; sed solum nobis unitur lumen solis ad visionem colorum.

Tertio, quia dato quod secundum modum praedictum uniretur nobis substantia intellectus agentis, tamen ipsi non ponunt quod intellectus agens totaliter uniatur nobis secundum unum intelligibile vel duo, sed secundum omnia intellecta speculata.

Sed omnia intellecta speculata deficiunt a virtute intellectus agentis, quia multo plus est intelligere substantias separatas, quam intelligere omnia materialia.

Unde manifestum est quod etiam intellectis omnibus materialibus, non sic uniretur intellectus agens nobis, ut possemus intelligere per eum substantias separatas. Quarto, quia intelligere omnia intellecta materialia vix contingit alicui in hoc mundo; et sic nullus, vel pauci ad felicitatem pervenirent.

Quod est contra philosophum, in I ethic., qui dicit quod felicitas est quoddam bonum commune, quod potest pervenire omnibus non orbatis ad virtutem.

Est etiam contra rationem quod finem alicuius speciei ut in paucioribus consequantur ea quae continentur sub specie.

Quinto, quia philosophus dicit expresse, in I ethic., quod felicitas est operatio secundum perfectam virtutem.

Et enumeratis multis virtutibus, in decimo, concludit quod felicitas ultima, consistens in cognitione maximorum intelligibilium, est secundum virtutem sapientiae, quam posuerat in sexto esse caput scientiarum speculativarum.

Unde patet quod Aristoteles posuit ultimam felicitatem hominis in cognitione substantiarum separatarum, qualis potest haberi per scientias speculativas, et non per continuationem intellectus agentis a quibusdam confictam.

Sexto, quia supra ostensum est quod intellectus agens non est substantia separata, sed virtus quaedam animae, ad eadem active se extendens, ad quae se extendit intellectus possibilis receptive, quia, ut dicitur in III de anima, intellectus possibilis est quo est omnia fieri, intellectus agens quo est omnia facere.

Uterque ergo intellectus se extendit, secundum statum praesentis vitae, ad materialia sola; quae intellectus agens facit intelligibilia actu, et recipiuntur in intellectu possibili.

Unde secundum statum praesentis vitae, neque per intellectum possibilem, neque per intellectum agentem, possumus intelligere substantias immateriales secundum seipsas.

Ad 1

Ad primum ergo dicendum quod ex illa auctoritate Augustini haberi potest quod illud quod mens nostra de cognitione incorporalium rerum accipere potest, per seipsam cognoscere possit. Et hoc adeo verum est, ut etiam apud philosophos dicatur quod scientia de anima est principium quoddam ad cognoscendum substantias separatas.

Per hoc enim quod anima nostra cognoscit seipsam, pertingit ad cognitionem aliquam habendam de substantiis incorporeis, qualem eam contingit habere, non quod simpliciter et perfecte eas cognoscat, cognoscendo seipsam.

Ad 2

Ad secundum dicendum quod similitudo naturae non est ratio sufficiens ad cognitionem, alioquin oporteret dicere quod empedocles dixit, quod anima esset de natura omnium, ad hoc quod omnia cognosceret.

Sed requiritur ad cognoscendum, ut sit similitudo rei cognitae in cognoscente quasi quaedam forma ipsius. Intellectus autem noster possibilis, secundum statum praesentis vitae, est natus informari similitudinibus rerum materialium a phantasmatibus abstractis, et ideo cognoscit magis materialia quam substantias immateriales.

Ad 3

Ad tertium dicendum quod requiritur aliqua proportio obiecti ad potentiam cognoscitivam, ut activi ad passivum, et perfectionis ad perfectibile. Unde quod excellentia sensibilia non capiantur a sensu, non sola ratio est quia corrumpunt organa sensibilia; sed etiam quia sunt improportionata potentiis sensitivis. Et hoc modo substantiae immateriales sunt improportionatae intellectui nostro, secundum praesentem statum, ut non possint ab eo intelligi.

Ad 4

Ad quartum dicendum quod illa ratio Commentatoris multipliciter deficit. Primo quidem, quia non sequitur quod, si substantiae separatae non intelliguntur a nobis, non intelligantur ab aliquo intellectu, intelliguntur enim a seipsis, et a se invicem.

Secundo, quia non est finis substantiarum separatarum ut intelligantur a nobis. Illud autem otiose et frustra esse dicitur, quod non consequitur finem ad quem est. Et sic non sequitur substantias immateriales esse frustra, etiam si nullo modo intelligerentur a nobis.

Ad 5

Ad quintum dicendum quod eodem modo sensus cognoscit et superiora et inferiora corpora, scilicet per immutationem organi a sensibili. Non autem eodem modo intelliguntur a nobis substantiae materiales, quae intelliguntur per modum abstractionis; et substantiae immateriales, quae non possunt sic a nobis intelligi, quia non sunt earum aliqua phantasmata.