Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that besides the intellectual soul there are in man other souls essentially different from one another, such as the sensitive soul and the nutritive soul. For corruptible and incorruptible are not of the same substance. But the intellectual soul is incorruptible; whereas the other souls, as the sensitive and the nutritive, are corruptible, as was shown above (Question 75, Article 6). Therefore in man the essence of the intellectual soul, the sensitive soul, and the nutritive soul, cannot be the same.

Objection 2: Further, if it be said that the sensitive soul in man is incorruptible; on the contrary, "corruptible and incorruptible differ generically," says the Philosopher, Metaph. x (Did. ix, 10). But the sensitive soul in the horse, the lion, and other brute animals, is corruptible. If, therefore, in man it be incorruptible, the sensitive soul in man and brute animals will not be of the same "genus." Now an animal is so called from its having a sensitive soul; and, therefore, "animal" will not be one genus common to man and other animals, which is absurd.

Objection 3: Further, the Philosopher says, Metaph. viii (Did. vii, 2), that the genus is taken from the matter, and difference from the form. But "rational," which is the difference constituting man, is taken from the intellectual soul; while he is called "animal" by reason of his having a body animated by a sensitive soul. Therefore the intellectual soul may be compared to the body animated by a sensitive soul, as form to matter. Therefore in man the intellectual soul is not essentially the same as the sensitive soul, but presupposes it as a material subject.

On the contrary, It is said in the book De Ecclesiasticis Dogmatibus xv: "Nor do we say that there are two souls in one man, as James and other Syrians write; one, animal, by which the body is animated, and which is mingled with the blood; the other, spiritual, which obeys the reason; but we say that it is one and the same soul in man, that both gives life to the body by being united to it, and orders itself by its own reasoning."

I answer that, Plato held that there were several souls in one body, distinct even as to organs, to which souls he referred the different vital actions, saying that the nutritive power is in the liver, the concupiscible in the heart, and the power of knowledge in the brain. Which opinion is rejected by Aristotle (De Anima ii, 2), with regard to those parts of the soul which use corporeal organs; for this reason, that in those animals which continue to live when they have been divided in each part are observed the operations of the soul, as sense and appetite. Now this would not be the case if the various principles of the soul's operations were essentially different, and distributed in the various parts of the body. But with regard to the intellectual part, he seems to leave it in doubt whether it be "only logically" distinct from the other parts of the soul, "or also locally."

The opinion of Plato might be maintained if, as he held, the soul was supposed to be united to the body, not as its form, but as its motor. For it involves nothing unreasonable that the same movable thing be moved by several motors; and still less if it be moved according to its various parts. If we suppose, however, that the soul is united to the body as its form, it is quite impossible for several essentially different souls to be in one body. This can be made clear by three different reasons.

In the first place, an animal would not be absolutely one, in which there were several souls. For nothing is absolutely one except by one form, by which a thing has existence: because a thing has from the same source both existence and unity; and therefore things which are denominated by various forms are not absolutely one; as, for instance, "a white man." If, therefore, man were 'living' by one form, the vegetative soul, and 'animal' by another form, the sensitive soul, and "man" by another form, the intellectual soul, it would follow that man is not absolutely one. Thus Aristotle argues, Metaph. viii (Did. vii, 6), against Plato, that if the idea of an animal is distinct from the idea of a biped, then a biped animal is not absolutely one. For this reason, against those who hold that there are several souls in the body, he asks (De Anima i, 5), "what contains them?"---that is, what makes them one? It cannot be said that they are united by the one body; because rather does the soul contain the body and make it one, than the reverse.

Secondly, this is proved to be impossible by the manner in which one thing is predicated of another. Those things which are derived from various forms are predicated of one another, either accidentally, (if the forms are not ordered to one another, as when we say that something white is sweet), or essentially, in the second manner of essential predication, (if the forms are ordered one to another, the subject belonging to the definition of the predicate; as a surface is presupposed to color; so that if we say that a body with a surface is colored, we have the second manner of essential predication.) Therefore, if we have one form by which a thing is an animal, and another form by which it is a man, it follows either that one of these two things could not be predicated of the other, except accidentally, supposing these two forms not to be ordered to one another---or that one would be predicated of the other according to the second manner of essential predication, if one soul be presupposed to the other. But both of these consequences are clearly false: because "animal" is predicated of man essentially and not accidentally; and man is not part of the definition of an animal, but the other way about. Therefore of necessity by the same form a thing is animal and man; otherwise man would not really be the thing which is an animal, so that animal can be essentially predicated of man.

Thirdly, this is shown to be impossible by the fact that when one operation of the soul is intense it impedes another, which could never be the case unless the principle of action were essentially one.

We must therefore conclude that in man the sensitive soul, the intellectual soul, and the nutritive soul are numerically one soul. This can easily be explained, if we consider the differences of species and forms. For we observe that the species and forms of things differ from one another, as the perfect and imperfect; as in the order of things, the animate are more perfect than the inanimate, and animals more perfect than plants, and man than brute animals; and in each of these genera there are various degrees. For this reason Aristotle, Metaph. viii (Did. vii, 3), compares the species of things to numbers, which differ in species by the addition or subtraction of unity. And (De Anima ii, 3) he compares the various souls to the species of figures, one of which contains another; as a pentagon contains and exceeds a tetragon. Thus the intellectual soul contains virtually whatever belongs to the sensitive soul of brute animals, and to the nutritive souls of plants. Therefore, as a surface which is of a pentagonal shape, is not tetragonal by one shape, and pentagonal by another---since a tetragonal shape would be superfluous as contained in the pentagonal---so neither is Socrates a man by one soul, and animal by another; but by one and the same soul he is both animal and man.

Reply to Objection 1: The sensitive soul is incorruptible, not by reason of its being sensitive, but by reason of its being intellectual. When, therefore, a soul is sensitive only, it is corruptible; but when with sensibility it has also intellectuality, it is incorruptible. For although sensibility does not give incorruptibility, yet it cannot deprive intellectuality of its incorruptibility.

Reply to Objection 2: Not forms, but composites, are classified either generically or specifically. Now man is corruptible like other animals. And so the difference of corruptible and incorruptible which is on the part of the forms does not involve a generic difference between man and the other animals.

Reply to Objection 3: The embryo has first of all a soul which is merely sensitive, and when this is removed, it is supplanted by a more perfect soul, which is both sensitive and intellectual: as will be shown further on (Question 118, Article 2, ad 2).

Reply to Objection 4: We must not consider the diversity of natural things as proceeding from the various logical notions or intentions, which flow from our manner of understanding, because reason can apprehend one and the same thing in various ways. Therefore since, as we have said, the intellectual soul contains virtually what belongs to the sensitive soul, and something more, reason can consider separately what belongs to the power of the sensitive soul, as something imperfect and material. And because it observes that this is something common to man and to other animals, it forms thence the notion of the "genus"; while that wherein the intellectual soul exceeds the sensitive soul, it takes as formal and perfecting; thence it gathers the "difference" of man.

Articulus 3

Argumentum 1

Ad tertium sic proceditur. Videtur quod praeter animam intellectivam sint in homine aliae animae per essentiam differentes, scilicet sensitiva et nutritiva.

Corruptibile enim et incorruptibile non sunt unius substantiae.

Sed anima intellectiva est incorruptibilis; aliae vero animae, scilicet sensitiva et nutritiva, sunt corruptibiles, ut ex superioribus patet.

Ergo in homine non potest esse una essentia animae intellectivae et sensitivae et nutritivae.

Argumentum 2

Si dicatur quod anima sensitiva in homine est incorruptibilis, contra, corruptibile et incorruptibile differunt secundum genus, ut dicitur in X metaphys..

Sed anima sensitiva in equo et leone et aliis brutis animalibus est corruptibilis. Si igitur in homine sit incorruptibilis, non erit eiusdem generis anima sensitiva in homine et bruto. Animal autem dicitur ex eo quod habet animam sensitivam. Neque ergo animal erit unum genus commune hominis et aliorum animalium. Quod est inconveniens.

Argumentum 3

Praeterea, philosophus dicit, in libro de generat. Animal., quod embryo prius est animal quam homo. Sed hoc esse non posset, si esset eadem essentia animae sensitivae et intellectivae, est enim animal per animam sensitivam, homo vero per animam intellectivam. Non ergo in homine est una essentia animae sensitivae et intellectivae.

Argumentum 4

Praeterea, philosophus dicit, in VIII metaphys., quod genus sumitur a materia, differentia vero a forma. Sed rationale, quod est differentia constitutiva hominis, sumitur ab anima intellectiva; animal vero dicitur ex hoc quod habet corpus animatum anima sensitiva. Anima ergo intellectiva comparatur ad corpus animatum anima sensitiva, sicut forma ad materiam. Non ergo anima intellectiva est eadem per essentiam cum anima sensitiva in homine; sed praesupponit eam sicut materiale suppositum.

Sed Contra

Sed contra est quod dicitur in libro de eccles. Dogmat., neque duas animas esse dicimus in homine uno, sicut Iacobus et alii syrorum scribunt, unam animalem, qua animatur corpus, et immixta sit sanguini, et alteram spiritualem, quae rationi ministret, sed dicimus unam et eandem esse animam in homine, quae et corpus sua societate vivificat, et semetipsam sua ratione disponit.

Corpus

Respondeo dicendum quod Plato posuit diversas animas esse in corpore uno, etiam secundum organa distinctas, quibus diversa opera vitae attribuebat; dicens vim nutritivam esse in hepate, concupiscibilem in corde, cognoscitivam in cerebro.

Quam quidem opinionem Aristoteles reprobat, in libro de anima, quantum ad illas animae partes quae corporeis organis in suis operibus utuntur, ex hoc quod in animalibus quae decisa vivunt, in qualibet parte inveniuntur diversae operationes animae, sicut sensus et appetitus. Hoc autem non esset, si diversa principia operationum animae, tanquam per essentiam diversae, diversis partibus corporis distributa essent. Sed de intellectiva sub dubio videtur relinquere utrum sit separata ab aliis partibus animae solum ratione, an etiam loco.

Opinio autem Platonis sustineri utique posset, si poneretur quod anima unitur corpori, non ut forma, sed ut motor, ut posuit Plato.

Nihil enim inconveniens sequitur, si idem mobile a diversis motoribus moveatur, praecipue secundum diversas partes. Sed si ponamus animam corpori uniri sicut formam, omnino impossibile videtur plures animas per essentiam differentes in uno corpore esse. Quod quidem triplici ratione manifestari potest.

Primo quidem, quia animal non esset simpliciter unum, cuius essent animae plures. Nihil enim est simpliciter unum nisi per formam unam, per quam habet res esse, ab eodem enim habet res quod sit ens et quod sit una; et ideo ea quae denominantur a diversis formis, non sunt unum simpliciter, sicut homo albus. Si igitur homo ab alia forma haberet quod sit vivum, scilicet ab anima vegetabili; et ab alia forma quod sit animal, scilicet ab anima sensibili; et ab alia quod sit homo, scilicet ab anima rationali; sequeretur quod homo non esset unum simpliciter, sicut et Aristoteles argumentatur contra Platonem, in VIII metaphys., quod si alia esset idea animalis, et alia bipedis, non esset unum simpliciter animal bipes. Et propter hoc, in I de anima, contra ponentes diversas animas in corpore, inquirit quid contineat illas, idest quid faciat ex eis unum.

Et non potest dici quod uniantur per corporis unitatem, quia magis anima continet corpus, et facit ipsum esse unum, quam e converso. Secundo, hoc apparet impossibile ex modo praedicationis. Quae enim sumuntur a diversis formis, praedicantur ad invicem vel per accidens, si formae non sint ad invicem ordinatae, puta cum dicimus quod album est dulce, vel, si formae sint ordinatae ad invicem, erit praedicatio per se, in secundo modo dicendi per se, quia subiectum ponitur in definitione praedicati. Sicut superficies praeambula est ad colorem, si ergo dicamus quod corpus superficiatum est coloratum, erit secundus modus praedicationis per se. Si ergo alia forma sit a qua aliquid dicitur animal, et a qua aliquid dicitur homo, sequeretur quod vel unum horum non possit praedicari de altero nisi per accidens, si istae duae formae ad invicem ordinem non habent; vel quod sit ibi praedicatio in secundo modo dicendi per se, si una animarum sit ad aliam praeambula. Utrumque autem horum est manifeste falsum, quia animal per se de homine praedicatur, non per accidens; homo autem non ponitur in definitione animalis, sed e converso. Ergo oportet eandem formam esse per quam aliquid est animal, et per quam aliquid est homo, alioquin homo non vere esset id quod est animal, ut sic animal per se de homine praedicetur.

Tertio, apparet hoc esse impossibile per hoc, quod una operatio animae, cum fuerit intensa, impedit aliam. Quod nullo modo contingeret, nisi principium actionum esset per essentiam unum.

Sic ergo dicendum quod eadem numero est anima in homine sensitiva et intellectiva et nutritiva. Quomodo autem hoc contingat, de facili considerari potest, si quis differentias specierum et formarum attendat. Inveniuntur enim rerum species et formae differre ab invicem secundum perfectius et minus perfectum, sicut in rerum ordine animata perfectiora sunt inanimatis, et animalia plantis, et homines animalibus brutis, et in singulis horum generum sunt gradus diversi.

Et ideo Aristoteles, in VIII metaphys., assimilat species rerum numeris, qui differunt specie secundum additionem vel subtractionem unitatis.

Et in II de anima, comparat diversas animas speciebus figurarum, quarum una continet aliam; sicut pentagonum continet tetragonum, et excedit.

Sic igitur anima intellectiva continet in sua virtute quidquid habet anima sensitiva brutorum, et nutritiva plantarum.

Sicut ergo superficies quae habet figuram pentagonam, non per aliam figuram est tetragona, et per aliam pentagona; quia superflueret figura tetragona, ex quo in pentagona continetur; ita nec per aliam animam socrates est homo, et per aliam animal, sed per unam et eandem.

Ad 1

Ad primum ergo dicendum quod anima sensitiva non habet incorruptibilitatem ex hoc quod est sensitiva, sed ex hoc quod est intellectiva, ei incorruptibilitas debetur. Quando ergo anima est sensitiva tantum, corruptibilis est, quando vero cum sensitivo intellectivum habet, est incorruptibilis. Licet enim sensitivum incorruptionem non det, tamen incorruptionem intellectivo auferre non potest.

Ad 2

Ad secundum dicendum quod formae non collocantur in genere vel in specie, sed composita. Homo autem corruptibilis est, sicut et alia animalia. Unde differentia secundum corruptibile et incorruptibile, quae est ex parte formarum, non facit hominem secundum genus ab aliis animalibus differre.

Ad 3

Ad tertium dicendum quod prius embryo habet animam quae est sensitiva tantum; qua abiecta, advenit perfectior anima, quae est simul sensitiva et intellectiva; ut infra plenius ostendetur.

Ad 4

Ad quartum dicendum quod non oportet secundum diversas rationes vel intentiones logicas, quae consequuntur modum intelligendi, diversitatem in rebus naturalibus accipere, quia ratio unum et idem secundum diversos modos apprehendere potest. Quia igitur, ut dictum est, anima intellectiva virtute continet id quod sensitiva habet, et adhuc amplius; potest seorsum ratio considerare quod pertinet ad virtutem sensitivae, quasi quoddam imperfectum et materiale. Et quia hoc invenit commune homini et aliis animalibus, ex hoc rationem generis format. Id vero in quo anima intellectiva sensitiva excedit, accipit quasi formale et completivum, et ex eo format differentiam hominis.