Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the human soul is not something subsistent. For that which subsists is said to be "this particular thing." Now "this particular thing" is said not of the soul, but of that which is composed of soul and body. Therefore the soul is not something subsistent.

Objection 2: Further, everything subsistent operates. But the soul does not operate; for, as the Philosopher says (De Anima i, 4), "to say that the soul feels or understands is like saying that the soul weaves or builds." Therefore the soul is not subsistent.

Objection 3: Further, if the soul were subsistent, it would have some operation apart from the body. But it has no operation apart from the body, not even that of understanding: for the act of understanding does not take place without a phantasm, which cannot exist apart from the body. Therefore the human soul is not something subsistent.

On the contrary, Augustine says (De Trin. x, 7): "Who understands that the nature of the soul is that of a substance and not that of a body, will see that those who maintain the corporeal nature of the soul, are led astray through associating with the soul those things without which they are unable to think of any nature---i.e. imaginary pictures of corporeal things." Therefore the nature of the human intellect is not only incorporeal, but it is also a substance, that is, something subsistent.

I answer that, It must necessarily be allowed that the principle of intellectual operation which we call the soul, is a principle both incorporeal and subsistent. For it is clear that by means of the intellect man can have knowledge of all corporeal things. Now whatever knows certain things cannot have any of them in its own nature; because that which is in it naturally would impede the knowledge of anything else. Thus we observe that a sick man's tongue being vitiated by a feverish and bitter humor, is insensible to anything sweet, and everything seems bitter to it. Therefore, if the intellectual principle contained the nature of a body it would be unable to know all bodies. Now every body has its own determinate nature. Therefore it is impossible for the intellectual principle to be a body. It is likewise impossible for it to understand by means of a bodily organ; since the determinate nature of that organ would impede knowledge of all bodies; as when a certain determinate color is not only in the pupil of the eye, but also in a glass vase, the liquid in the vase seems to be of that same color.

Therefore the intellectual principle which we call the mind or the intellect has an operation "per se" apart from the body. Now only that which subsists can have an operation "per se." For nothing can operate but what is actual: for which reason we do not say that heat imparts heat, but that what is hot gives heat. We must conclude, therefore, that the human soul, which is called the intellect or the mind, is something incorporeal and subsistent.

Reply to Objection 1: "This particular thing" can be taken in two senses. Firstly, for anything subsistent; secondly, for that which subsists, and is complete in a specific nature. The former sense excludes the inherence of an accident or of a material form; the latter excludes also the imperfection of the part, so that a hand can be called "this particular thing" in the first sense, but not in the second. Therefore, as the human soul is a part of human nature, it can indeed be called "this particular thing," in the first sense, as being something subsistent; but not in the second, for in this sense, what is composed of body and soul is said to be "this particular thing."

Reply to Objection 2: Aristotle wrote those words as expressing not his own opinion, but the opinion of those who said that to understand is to be moved, as is clear from the context. Or we may reply that to operate "per se" belongs to what exists "per se." But for a thing to exist "per se," it suffices sometimes that it be not inherent, as an accident or a material form; even though it be part of something. Nevertheless, that is rightly said to subsist "per se," which is neither inherent in the above sense, nor part of anything else. In this sense, the eye or the hand cannot be said to subsist "per se"; nor can it for that reason be said to operate "per se." Hence the operation of the parts is through each part attributed to the whole. For we say that man sees with the eye, and feels with the hand, and not in the same sense as when we say that what is hot gives heat by its heat; for heat, strictly speaking, does not give heat. We may therefore say that the soul understands, as the eye sees; but it is more correct to say that man understands through the soul.

Reply to Objection 3: The body is necessary for the action of the intellect, not as its origin of action, but on the part of the object; for the phantasm is to the intellect what color is to the sight. Neither does such a dependence on the body prove the intellect to be non-subsistent; otherwise it would follow that an animal is non-subsistent, since it requires external objects of the senses in order to perform its act of perception.

Articulus 2

Argumentum 1

Ad secundum sic proceditur. Videtur quod anima humana non sit aliquid subsistens. Quod enim est subsistens, dicitur hoc aliquid.

Anima autem non est hoc aliquid, sed compositum ex anima et corpore. Ergo anima non est aliquid subsistens.

Argumentum 2

Praeterea, omne quod est subsistens, potest dici operari.

Sed anima non dicitur operari, quia, ut dicitur in I de anima, dicere animam sentire aut intelligere, simile est ac si dicat eam aliquis texere vel aedificare.

Ergo anima non est aliquid subsistens.

Argumentum 3

Praeterea, si anima esset aliquid subsistens, esset aliqua eius operatio sine corpore. Sed nulla est eius operatio sine corpore, nec etiam intelligere, quia non contingit intelligere sine phantasmate, phantasma autem non est sine corpore.

Ergo anima humana non est aliquid subsistens.

Sed Contra

Sed contra est quod Augustinus dicit, X de Trin..

Quisquis videt mentis naturam et esse substantiam, et non esse corpoream, videt eos qui opinantur eam esse corpoream, ob hoc errare, quod adiungunt ei ea sine quibus nullam possunt cogitare naturam, scilicet corporum phantasias.

Natura ergo mentis humanae non solum est incorporea, sed etiam substantia, scilicet aliquid subsistens.

Corpus

Respondeo dicendum quod necesse est dicere id quod est principium intellectualis operationis, quod dicimus animam hominis, esse quoddam principium incorporeum et subsistens. Manifestum est enim quod homo per intellectum cognoscere potest naturas omnium corporum. Quod autem potest cognoscere aliqua, oportet ut nihil eorum habeat in sua natura, quia illud quod inesset ei naturaliter impediret cognitionem aliorum; sicut videmus quod lingua infirmi quae infecta est cholerico et amaro humore, non potest percipere aliquid dulce, sed omnia videntur ei amara. Si igitur principium intellectuale haberet in se naturam alicuius corporis, non posset omnia corpora cognoscere. Omne autem corpus habet aliquam naturam determinatam. Impossibile est igitur quod principium intellectuale sit corpus.

Et similiter impossibile est quod intelligat per organum corporeum, quia etiam natura determinata illius organi corporei prohiberet cognitionem omnium corporum; sicut si aliquis determinatus color sit non solum in pupilla, sed etiam in vase vitreo, liquor infusus eiusdem coloris videtur.

Ipsum igitur intellectuale principium, quod dicitur mens vel intellectus, habet operationem per se, cui non communicat corpus.

Nihil autem potest per se operari, nisi quod per se subsistit.

Non enim est operari nisi entis in actu, unde eo modo aliquid operatur, quo est. Propter quod non dicimus quod calor calefacit, sed calidum. Relinquitur igitur animam humanam, quae dicitur intellectus vel mens, esse aliquid incorporeum et subsistens.

Ad 1

Ad primum ergo dicendum quod hoc aliquid potest accipi dupliciter, uno modo, pro quocumque subsistente, alio modo, pro subsistente completo in natura alicuius speciei. Primo modo, excludit inhaerentiam accidentis et formae materialis, secundo modo, excludit etiam imperfectionem partis. Unde manus posset dici hoc aliquid primo modo, sed non secundo modo. Sic igitur, cum anima humana sit pars speciei humanae, potest dici hoc aliquid primo modo, quasi subsistens, sed non secundo modo, sic enim compositum ex anima et corpore dicitur hoc aliquid.

Ad 2

Ad secundum dicendum quod verba illa Aristoteles dicit non secundum propriam sententiam, sed secundum opinionem illorum qui dicebant quod intelligere est moveri; ut patet ex iis quae ibi praemittit.

Vel dicendum quod per se agere convenit per se existenti. Sed per se existens quandoque potest dici aliquid si non sit inhaerens ut accidens vel ut forma materialis, etiam si sit pars. Sed proprie et per se subsistens dicitur quod neque est praedicto modo inhaerens, neque est pars. Secundum quem modum oculus aut manus non posset dici per se subsistens; et per consequens nec per se operans. Unde et operationes partium attribuuntur toti per partes. Dicimus enim quod homo videt per oculum, et palpat per manum, aliter quam calidum calefacit per calorem, quia calor nullo modo calefacit, proprie loquendo.

Potest igitur dici quod anima intelligit, sicut oculus videt, sed magis proprie dicitur quod homo intelligat per animam.

Ad 3

Ad tertium dicendum quod corpus requiritur ad actionem intellectus, non sicut organum quo talis actio exerceatur, sed ratione obiecti, phantasma enim comparatur ad intellectum sicut color ad visum. Sic autem indigere corpore non removet intellectum esse subsistentem, alioquin animal non esset aliquid subsistens, cum indigeat exterioribus sensibilibus ad sentiendum.