Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that no bodies are active. For Augustine says (De Civ. Dei v, 9): "There are things that are acted upon, but do not act; such are bodies: there is one Who acts but is not acted upon; this is God: there are things that both act and are acted upon; these are the spiritual substances."

Objection 2: Further, every agent except the first agent requires in its work a subject susceptible of its action. But there is not substance below the corporeal substance which can be susceptible of the latter's action; since it belongs to the lowest degree of beings. Therefore corporeal substance is not active.

Objection 3: Further, every corporeal substance is limited by quantity. But quantity hinders substance from movement and action, because it surrounds it and penetrates it: just as a cloud hinders the air from receiving light. A proof of this is that the more a body increases in quantity, the heavier it is and the more difficult to move. Therefore no corporeal substance is active.

Objection 4: Further, the power of action in every agent is according to its propinquity to the first active cause. But bodies, being most composite, are most remote from the first active cause, which is most simple. Therefore no bodies are active.

Objection 5: Further, if a body is an agent, the term of its action is either a substantial, or an accidental form. But it is not a substantial form; for it is not possible to find in a body any principle of action, save an active quality, which is an accident; and an accident cannot be the cause of a substantial form, since the cause is always more excellent than the effect. Likewise, neither is it an accidental form, for "an accident does not extend beyond its subject," as Augustine says (De Trin. ix, 4). Therefore no bodies are active.

On the contrary, Dionysius says (Coel. Hier. xv) that among other qualities of corporeal fire, "it shows its greatness in its action and power on that of which it lays hold."

I answer that, It is apparent to the senses that some bodies are active. But concerning the action of bodies there have been three errors. For some denied all action to bodies. This is the opinion of Avicebron in his book on The Fount of Life, where, by the arguments mentioned above, he endeavors to prove that no bodies act, but that all the actions which seem to be the actions of bodies, are the actions of some spiritual power that penetrates all bodies: so that, according to him, it is not fire that heats, but a spiritual power which penetrates, by means of the fire. And this opinion seems to be derived from that of Plato. For Plato held that all forms existing in corporeal matter are participated thereby, and determined and limited thereto; and that separate forms are absolute and as it were universal; wherefore he said that these separate forms are the causes of forms that exist in matter. Therefore inasmuch as the form which is in corporeal matter is determined to this matter individualized by quantity, Avicebron held that the corporeal form is held back and imprisoned by quantity, as the principle of individuality, so as to be unable by action to extend to any other matter: and that the spiritual and immaterial form alone, which is not hedged in by quantity, can issue forth by acting on something else.

But this does not prove that the corporeal form is not an agent, but that it is not a universal agent. For in proportion as a thing is participated, so, of necessity, must that be participated which is proper thereto; thus in proportion to the participation of light is the participation of visibility. But to act, which is nothing else than to make something to be in act, is essentially proper to an act as such; wherefore every agent produces its like. So therefore to the fact of its being a form not determined by matter subject to quantity, a thing owes its being an agent indeterminate and universal: but to the fact that it is determined to this matter, it owes its being an agent limited and particular. Wherefore if the form of fire were separate, as the Platonists supposed, it would be, in a fashion, the cause of every ignition. But this form of fire which is in this corporeal matter, is the cause of this ignition which passes from this body to that. Hence such an action is effected by the contact of two bodies.

But this opinion of Avicebron goes further than that of Plato. For Plato held only substantial forms to be separate; while he referred accidents to the material principles which are "the great" and "the small," which he considered to be the first contraries, by others considered to the "the rare" and "the dense." Consequently both Plato and Avicenna, who follows him to a certain extent, held that corporeal agents act through their accidental forms, by disposing matter for the substantial form; but that the ultimate perfection attained by the introduction of the substantial form is due to an immaterial principle. And this is the second opinion concerning the action of bodies; of which we have spoken above when treating of the creation (Question 45, Article 8).

The third opinion is that of Democritus, who held that action takes place through the issue of atoms from the corporeal agent, while passion consists in the reception of the atoms in the pores of the passive body. This opinion is disproved by Aristotle (De Gener. i, 8,9). For it would follow that a body would not be passive as a whole, and the quantity of the active body would be diminished through its action; which things are manifestly untrue.

We must therefore say that a body acts forasmuch as it is in act, on a body forasmuch as it is in potentiality.

Reply to Objection 1: This passage of Augustine is to be understood of the whole corporeal nature considered as a whole, while thus has no nature inferior to it, on which it can act; as the spiritual nature acts on the corporeal, and the uncreated nature on the created. Nevertheless one body is inferior to another, forasmuch as it is in potentiality to that which the other has in act.

From this follows the solution of the second objection. But it must be observed, when Avicebron argues thus, "There is a mover who is not moved, to wit, the first maker of all; therefore, on the other hand, there exists something moved which is purely passive," that this is to be conceded. But this latter is primary matter, which is a pure potentiality, just as God is pure act. Now a body is composed of potentiality and act; and therefore it is both active and passive.

Reply to Objection 3: Quantity does not entirely hinder the corporeal form from action, as stated above; but from being a universal agent, forasmuch as a form is individualized through being in matter subject to quantity. The proof taken from the weight of bodies is not to the purpose. First, because addition of quantity does not cause weight; as is proved (De Coelo et Mundo iv, 2). Secondly, it is false that weight retards movement; on the contrary, the heavier a thing, the greater its movement, if we consider the movement proper thereto. Thirdly, because action is not effected by local movement, as Democritus held: but by something being reduced from potentiality to act.

Reply to Objection 4: A body is not that which is most distant from God; for it participates something of a likeness to the Divine Being, forasmuch as it has a form. That which is most distant from God is primary matter; which is in no way active, since it is a pure potentiality.

Reply to Objection 5: The term of a body's action is both an accidental form and a substantial form. For the active quality, such as heat, although itself an accident, acts nevertheless by virtue of the substantial form, as its instrument: wherefore its action can terminate in a substantial form; thus natural heat, as the instrument of the soul, has an action terminating in the generation of flesh. But by its own virtue it produces an accident. Nor is it against the nature of an accident to surpass its subject in acting, but it is to surpass it in being; unless indeed one were to imagine that an accident transfers its identical self from the agent to the patient; thus Democritus explained action by an issue of atoms.

Articulus 1

Argumentum 1

Ad primum sic proceditur. Videtur quod nullum corpus sit activum.

Dicit enim Augustinus quod in rebus invenitur aliquid actum et non agens, sicut sunt corpora; aliquid agens et non actum, sicut deus; aliquid agens et actum, sicut substantiae spirituales.

Argumentum 2

Praeterea, omne agens, excepto primo agente, in suo opere indiget subiecto quod sit susceptibile suae actionis. Sed infra substantiam corporalem non est substantia quae sit susceptibilis suae actionis, quia haec substantia tenet infimum gradum in entibus. Ergo substantia corporalis non est activa.

Argumentum 3

Praeterea, omnis substantia corporalis concluditur quantitate.

Sed quantitas impedit substantiam a motu et actione, quia comprehendit eam, et mergitur in ea, sicut impeditur aer nubilosus a perceptione luminis. Et huius signum est, quod quanto magis accreverit quantitas corporis, tanto est ponderosius et gravius ad hoc quod moveatur.

Ergo nulla substantia corporalis est activa.

Argumentum 4

Praeterea, omne agens habet virtutem agendi ex propinquitate ad primum activum. Sed a primo activo, quod est simplicissimum, remotissima sunt corpora, quae sunt maxime composita.

Ergo nullum corpus est agens.

Argumentum 5

Praeterea, si aliquod corpus est agens, aut agit ad formam substantialem; aut ad formam accidentalem. Sed non ad formam substantialem, quia non invenitur in corporibus principium actionis nisi aliqua qualitas activa, quae est accidens; accidens autem non potest esse causa formae substantialis, cum causa sit potior quam effectus. Similiter etiam neque ad formam accidentalem, quia accidens non se extendit ultra suum subiectum, ut Augustinus dicit IX de Trin..

Ergo nullum corpus est activum.

Sed Contra

Sed contra est quod dionysius, XV cap. Cael. Hier., inter ceteras proprietates corporei ignis, dicit quod ad susceptas materias manifestat sui ipsius magnitudinem activus et potens.

Corpus

Respondeo dicendum quod sensibiliter apparet aliqua corpora esse activa. Sed circa corporum actiones tripliciter aliqui erraverunt.

Fuerunt enim aliqui qui totaliter corporibus actiones subtraxerunt. Et haec est opinio Avicebron in libro fontis vitae, ubi per rationes quae tactae sunt, probare nititur quod nullum corpus agit, sed omnes actiones quae videntur esse corporum, sunt actiones cuiusdam virtutis spiritualis quae penetrat per omnia corpora; ita quod ignis, secundum eum, non calefacit, sed virtus spiritualis penetrans per ipsum.

Et videtur haec opinio derivata esse ab opinione Platonis. Nam Plato posuit omnes formas quae sunt in materia corporali, esse participatas et determinatas et contractas ad hanc materiam; formas vero separatas esse absolutas et quasi universales; et ideo illas formas separatas dicebat esse causas formarum quae sunt in materia. Secundum hoc ergo quod forma quae est in materia corporali, determinata est ad hanc materiam individuatam per quantitatem, ponebat Avicebron quod a quantitate, prout est individuationis principium, retinetur et arcetur forma corporalis, ne possit se extendere per actionem in aliam materiam; sed solum forma spiritualis et immaterialis, quae non est coarctata per quantitatem, potest effluere per actionem in aliud.

Sed ista ratio non concludit quod forma corporalis non sit agens, sed quod non sit agens universale. Secundum enim quod participatur aliquid, secundum hoc est necessarium quod participetur id quod est proprium ei, sicut quantum participatur de lumine, tantum participatur de ratione visibilis. Agere autem, quod nihil est aliud quam facere aliquid actu, est per se proprium actus, inquantum est actus, unde et omne agens agit sibi simile.

Sic ergo ex hoc quod aliquid est forma non determinata per materiam quantitati subiectam, habet quod sit agens indeterminatum et universale, ex hoc vero quod est determinata ad hanc materiam, habet quod sit agens contractum et particulare. Unde si esset forma ignis separata, ut Platonici posuerunt, esset aliquo modo causa omnis ignitionis. Sed haec forma ignis quae est in hac materia corporali, est causa huius ignitionis quae est ab hoc corpore in hoc corpus. Unde et fit talis actio per contactum duorum corporum. Sed tamen haec opinio Avicebron superexcedit opinionem Platonis. Nam Plato ponebat solum formas substantiales separatas; accidentia vero reducebat ad principia materialia quae sunt magnum et parvum, quae ponebat esse prima contraria, sicut et alii rarum et densum.

Et ideo tam Plato quam Avicenna, in aliquo ipsum sequens, ponebant quod agentia corporalia agunt secundum formas accidentales, disponendo materiam ad formam substantialem; sed ultima perfectio, quae est per introductionem formae substantialis est a principio immateriali. Et haec est secunda opinio de actione corporum, de qua supra dictum est, cum de creatione ageretur.

Tertia vero opinio fuit democriti, qui ponebat actionem esse per effluxionem atomorum a corpore agente, et passionem esse per receptionem eorundem in poris corporis patientis.

Quam opinionem improbat Aristoteles in I de generat..

Sequeretur enim quod corpus non pateretur per totum, et quod quantitas corporis agentis diminueretur ex hoc quod agit, quae sunt manifeste falsa. Dicendum est ergo quod corpus agit secundum quod est actu, in aliud corpus secundum quod est in potentia.

Ad 1

Ad primum ergo dicendum quod dictum Augustini est intelligendum de tota natura corporali simul accepta, quae non habet aliquam inferiorem naturam infra se, in quam agat, sicut natura spiritualis in corporalem, et natura increata in creatam. Sed tamen unum corpus est infra alterum, inquantum est in potentia ad id quod habet aliud in actu.

Ad 2

Et per hoc patet solutio ad secundum. Sciendum est tamen quod, cum Avicebron sic argumentatur, est aliquid quod est movens non motum, scilicet primus factor rerum, ergo, ex opposito, est aliquid quod est motum et patiens tantum, quod concedendum est. Sed hoc est materia prima, quae est potentia pura, sicut deus est actus purus. Corpus autem componitur ex potentia et actu, et ideo est agens et patiens.

Ad 3

Ad tertium dicendum quod quantitas non impedit formam corporalem omnino ab actione, sicut dictum est, sed impedit eam ne sit agens universale, inquantum forma individuatur prout est in materia quantitati subiecta. Signum tamen quod inducitur de ponderositate corporum, non est ad propositum. Primo quidem, quia additio quantitatis non est causa gravitatis; ut probatur in IV de caelo et mundo.

Secundo, quia falsum est quod ponderositas facit tardiorem motum, immo quanto aliquid est gravius, tanto magis movetur motu proprio. Tertio, quia actio non fit per motum localem, ut democritus posuit; sed per hoc quod aliquid reducitur de potentia in actum.

Ad 4

Ad quartum dicendum quod corpus non est id quod maxime distat a deo, participat enim aliquid de similitudine divini esse, secundum formam quam habet. Sed id quod maxime distat a deo, est materia prima; quae nullo modo est agens, cum sit in potentia tantum.

Ad 5

Ad quintum dicendum quod corpus agit et ad formam accidentalem, et ad formam substantialem. Qualitas enim activa, ut calor, etsi sit accidens, agit tamen in virtute formae substantialis, sicut eius instrumentum; et ideo potest agere ad formam substantialem; sicut et calor naturalis, inquantum est instrumentum animae, agit ad generationem carnis. Ad accidens vero agit propria virtute.

Nec est contra rationem accidentis, quod excedat suum subiectum in agendo, sed quod excedat in essendo, nisi forsan quis imaginetur idem accidens numero defluere ab agente in patiens, sicut democritus ponebat fieri actionem per defluxum atomorum.