Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the intellectual soul is improperly united to such a body. For matter must be proportionate to the form. But the intellectual soul is incorruptible. Therefore it is not properly united to a corruptible body.

Objection 2: Further, the intellectual soul is a perfectly immaterial form; a proof whereof is its operation in which corporeal matter does not share. But the more subtle is the body, the less has it of matter. Therefore the soul should be united to a most subtle body, to fire, for instance, and not to a mixed body, still less to a terrestrial body.

Objection 3: Further, since the form is the principle of the species, one form cannot produce a variety of species. But the intellectual soul is one form. Therefore, it should not be united to a body which is composed of parts belonging to various species.

Objection 4: Further, what is susceptible of a more perfect form should itself be more perfect. But the intellectual soul is the most perfect of souls. Therefore since the bodies of other animals are naturally provided with a covering, for instance, with hair instead of clothes, and hoofs instead of shoes; and are, moreover, naturally provided with arms, as claws, teeth, and horns; it seems that the intellectual soul should not have been united to a body which is imperfect as being deprived of the above means of protection.

On the contrary, The Philosopher says (De Anima ii, 1), that "the soul is the act of a physical organic body having life potentially."

I answer that, Since the form is not for the matter, but rather the matter for the form, we must gather from the form the reason why the matter is such as it is; and not conversely. Now the intellectual soul, as we have seen above (Question 55, Article 2) in the order of nature, holds the lowest place among intellectual substances; inasmuch as it is not naturally gifted with the knowledge of truth, as the angels are; but has to gather knowledge from individual things by way of the senses, as Dionysius says (Div. Nom. vii). But nature never fails in necessary things: therefore the intellectual soul had to be endowed not only with the power of understanding, but also with the power of feeling. Now the action of the senses is not performed without a corporeal instrument. Therefore it behooved the intellectual soul to be united to a body fitted to be a convenient organ of sense.

Now all the other senses are based on the sense of touch. But the organ of touch requires to be a medium between contraries, such as hot and cold, wet and dry, and the like, of which the sense of touch has the perception; thus it is in potentiality with regard to contraries, and is able to perceive them. Therefore the more the organ of touch is reduced to an equable complexion, the more sensitive will be the touch. But the intellectual soul has the power of sense in all its completeness; because what belongs to the inferior nature pre-exists more perfectly in the superior, as Dionysius says (Div. Nom. v). Therefore the body to which the intellectual soul is united should be a mixed body, above others reduced to the most equable complexion. For this reason among animals, man has the best sense of touch. And among men, those who have the best sense of touch have the best intelligence. A sign of which is that we observe "those who are refined in body are well endowed in mind," as stated in De Anima ii, 9.

Reply to Objection 1: Perhaps someone might attempt to answer this by saying that before sin the human body was incorruptible. This answer does not seem sufficient; because before sin the human body was immortal not by nature, but by a gift of Divine grace; otherwise its immortality would not be forfeited through sin, as neither was the immortality of the devil.

Therefore we answer otherwise by observing that in matter two conditions are to be found; one which is chosen in order that the matter be suitable to the form; the other which follows by force of the first disposition. The artisan, for instance, for the form of the saw chooses iron adapted for cutting through hard material; but that the teeth of the saw may become blunt and rusted, follows by force of the matter itself. So the intellectual soul requires a body of equable complexion, which, however, is corruptible by force of its matter. If, however, it be said that God could avoid this, we answer that in the formation of natural things we do not consider what God might do; but what is suitable to the nature of things, as Augustine says (Gen. ad lit. ii, 1). God, however, provided in this case by applying a remedy against death in the gift of grace.

Reply to Objection 2: A body is not necessary to the intellectual soul by reason of its intellectual operation considered as such; but on account of the sensitive power, which requires an organ of equable temperament. Therefore the intellectual soul had to be united to such a body, and not to a simple element, or to a mixed body, in which fire was in excess; because otherwise there could not be an equability of temperament. And this body of an equable temperament has a dignity of its own by reason of its being remote from contraries, thereby resembling in a way a heavenly body.

Reply to Objection 3: The parts of an animal, for instance, the eye, hand, flesh, and bones, and so forth, do not make the species; but the whole does, and therefore, properly speaking, we cannot say that these are of different species, but that they are of various dispositions. This is suitable to the intellectual soul, which, although it be one in its essence, yet on account of its perfection, is manifold in power: and therefore, for its various operations it requires various dispositions in the parts of the body to which it is united. For this reason we observe that there is a greater variety of parts in perfect than in imperfect animals; and in these a greater variety than in plants.

Reply to Objection 4: The intellectual soul as comprehending universals, has a power extending to the infinite; therefore it cannot be limited by nature to certain fixed natural notions, or even to certain fixed means whether of defence or of clothing, as is the case with other animals, the souls of which are endowed with knowledge and power in regard to fixed particular things. Instead of all these, man has by nature his reason and his hands, which are "the organs of organs" (De Anima iii), since by their means man can make for himself instruments of an infinite variety, and for any number of purposes.

Articulus 5

Argumentum 1

Ad quintum sic proceditur. Videtur quod anima intellectiva inconvenienter tali corpori uniatur. Materia enim debet esse proportionata formae. Sed anima intellectiva est forma incorruptibilis. Non ergo convenienter unitur corpori corruptibili.

Argumentum 2

Praeterea, anima intellectiva est forma maxime immaterialis, cuius signum est, quod habet operationem in qua non communicat materia corporalis. Sed quanto corpus est subtilius, tanto minus habet de materia. Ergo anima deberet subtilissimo corpori uniri, puta igni; et non corpori mixto, et terrestri magis.

Argumentum 3

Praeterea, cum forma sit principium speciei, ab una forma non proveniunt diversae species. Sed anima intellectiva est una forma. Ergo non debet uniri corpori quod componitur ex partibus dissimilium specierum.

Argumentum 4

Praeterea, perfectioris formae debet esse perfectius susceptibile.

Sed anima intellectiva est perfectissima animarum. Cum igitur aliorum animalium corpora habeant naturaliter insita tegumenta, puta pilorum loco vestium, et unguium loco calceamentorum; habeant etiam arma naturaliter sibi data, sicut ungues, dentes et cornua, ergo videtur quod anima intellectiva non debuerit uniri corpori imperfecto tanquam talibus auxiliis privato.

Sed Contra

Sed contra est quod dicit philosophus, in II de anima, quod anima est actus corporis physici organici potentia vitam habentis.

Corpus

Respondeo dicendum quod, cum forma non sit propter materiam, sed potius materia propter formam; ex forma oportet rationem accipere quare materia sit talis, et non e converso. Anima autem intellectiva, sicut supra habitum est, secundum naturae ordinem, infimum gradum in substantiis intellectualibus tenet; intantum quod non habet naturaliter sibi inditam notitiam veritatis, sicut Angeli, sed oportet quod eam colligat ex rebus divisibilibus per viam sensus, ut dionysius dicit, VII cap. De div. Nom..

Natura autem nulli deest in necessariis, unde oportuit quod anima intellectiva non solum haberet virtutem intelligendi, sed etiam virtutem sentiendi. Actio autem sensus non fit sine corporeo instrumento. Oportuit igitur animam intellectivam tali corpori uniri, quod possit esse conveniens organum sensus.

Omnes autem alii sensus fundantur supra tactum. Ad organum autem tactus requiritur quod sit medium inter contraria, quae sunt calidum et frigidum, humidum et siccum, et similia, quorum est tactus apprehensivus, sic enim est in potentia ad contraria, et potest ea sentire. Unde quanto organum tactus fuerit magis reductum ad aequalitatem complexionis, tanto perceptibilior erit tactus. Anima autem intellectiva habet completissime virtutem sensitivam, quia quod est inferioris praeexistit perfectius in superiori ut dicit dionysius in libro de div. Nom..

Unde oportuit corpus cui unitur anima intellectiva, esse corpus mixtum, inter omnia alia magis reductum ad aequalitatem complexionis. Et propter hoc homo inter omnia animalia melioris est tactus. Et inter ipsos homines, qui sunt melioris tactus, sunt melioris intellectus.

Cuius signum est, quod molles carne bene aptos mente videmus, ut dicitur in II de anima.

Ad 1

Ad primum ergo dicendum quod hanc obiectionem aliquis forte vellet evadere per hoc, quod diceret corpus hominis ante peccatum incorruptibile fuisse. Sed haec responsio non videtur sufficiens, quia corpus hominis ante peccatum immortale fuit non per naturam, sed per gratiae divinae donum; alioquin immortalitas eius per peccatum sublata non esset, sicut nec immortalitas Daemonis. Et ideo aliter dicendum est, quod in materia duplex conditio invenitur, una quae eligitur ad hoc quod sit conveniens formae; alia quae ex necessitate consequitur prioris dispositionis. Sicut artifex ad formam serrae eligit materiam ferream, aptam ad secandum dura; sed quod dentes serrae hebetari possint et rubiginem contrahere, sequitur ex necessitate materiae. Sic igitur et animae intellectivae debetur corpus quod sit aequalis complexionis, ex hoc autem de necessitate materiae sequitur quod sit corruptibile. Si quis vero dicat quod deus potuit hanc necessitatem vitare, dicendum est quod in constitutione rerum naturalium non consideratur quid deus facere possit, sed quid naturae rerum conveniat, ut Augustinus dicit, II super Gen. Ad litt..

Providit tamen deus adhibendo remedium contra mortem per gratiae donum.

Ad 2

Ad secundum dicendum quod animae intellectivae non debetur corpus propter ipsam intellectualem operationem secundum se; sed propter sensitivam virtutem, quae requirit organum aequaliter complexionatum. Et ideo oportuit animam intellectivam tali corpori uniri, et non simplici elemento, vel corpori mixto in quo excederet ignis secundum quantitatem, quia non posset esse aequalitas complexionis, propter excedentem ignis activam virtutem. Habet autem hoc corpus aequaliter complexionatum quandam dignitatem, per hoc quod est remotum a contrariis; in quo quodammodo assimilatur corpori caelesti.

Ad 3

Ad tertium dicendum quod partes animalis, ut oculus, manus, caro et os, et huiusmodi, non sunt in specie, sed totum, et ideo non potest dici, proprie loquendo, quod sint diversarum specierum, sed quod sint diversarum dispositionum. Et hoc competit animae intellectivae, quae quamvis sit una secundum essentiam, tamen propter sui perfectionem est multiplex in virtute; et ideo, ad diversas operationes, indiget diversis dispositionibus in partibus corporis cui unitur. Et propter hoc videmus quod maior est diversitas partium in animalibus perfectis quam in imperfectis, et in his quam in plantis.

Ad 4

Ad quartum dicendum quod anima intellectiva, quia est universalium comprehensiva, habet virtutem ad infinita. Et ideo non potuerunt sibi determinari a natura vel determinatae existimationes naturales, vel etiam determinata auxilia vel defensionum vel tegumentorum; sicut aliis animalibus, quorum animae habent apprehensionem et virtutem ad aliqua particularia determinata. Sed loco horum omnium, homo habet naturaliter rationem, et manus, quae sunt organa organorum, quia per eas homo potest sibi praeparare instrumenta infinitorum modorum, et ad infinitos effectus.