# Summa Theologiae/First Part/Question 115
## Treatise on The Conservation And Government Of Creatures
### question. 115 - OF THE ACTION OF THE CORPOREAL CREATURE (SIX ARTICLES)

We have now to consider the action of the corporeal creature; and fate, which is ascribed to certain bodies. Concerning corporeal actions there are six points of inquiry:
(1) Whether a body can be active?
(2) Whether there exist in bodies certain seminal virtues?
(3) Whether the heavenly bodies are the causes of what is done here by the inferior bodies?
(4) Whether they are the cause of human acts?
(5) Whether demons are subject to their influence?
(6) Whether the heavenly bodies impose necessity on those things which are subject to their influence?

#### Art. 1 - Whether a body can be active?

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 (Q[45], A[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.

#### Art. 2 - Whether there are any seminal virtues in corporeal matter?

Objection 1: It would seem that there are no seminal virtues in corporeal matter. For virtue [ratio] implies something of a spiritual order. But in corporeal matter nothing exists spiritually, but only materially, that is, according to the mode of that in which it is. Therefore there are no seminal virtues in corporeal matter.
Objection 2: Further, Augustine (De Trin. iii, 8,9) says that demons produce certain results by employing with a hidden movement certain seeds, which they know to exist in matter. But bodies, not virtues, can be employed with local movement. Therefore it is unreasonable to say that there are seminal virtues in corporeal matter.
Objection 3: Further, seeds are active principles. But there are no active principles in corporeal matter; since, as we have said above, matter is not competent to act (A[1], ad 2,4). Therefore there are no seminal virtues in corporeal matter.
Objection 4: Further, there are said to be certain "causal virtues" (Augustine, De Gen. ad lit. v, 4) which seem to suffice for the production of things. But seminal virtues are not causal virtues: for miracles are outside the scope of seminal virtues, but not of causal virtues. Therefore it is unreasonable to say that there are seminal virtues in corporeal matter.
On the contrary, Augustine says (De Trin. iii, 8): "Of all the things which are generated in a corporeal and visible fashion, certain seeds lie hidden in the corporeal things of this world."
I answer that, It is customary to name things after what is more perfect, as the Philosopher says (De Anima ii, 4). Now in the whole corporeal nature, living bodies are the most perfect: wherefore the word "nature" has been transferred from living things to all natural things. For the word itself, "nature," as the Philosopher says (Metaph. v, Did. iv, 4), was first applied to signify the generation of living things, which is called "nativity": and because living things are generated from a principle united to them, as fruit from a tree, and the offspring from the mother, to whom it is united, consequently the word "nature" has been applied to every principle of movement existing in that which is moved. Now it is manifest that the active and passive principles of the generation of living things are the seeds from which living things are generated. Therefore Augustine fittingly gave the name of "seminal virtues" [seminales rationes] to all those active and passive virtues which are the principles of natural generation and movement.
These active and passive virtues may be considered in several orders. For in the first place, as Augustine says (Gen. ad lit. vi, 10), they are principally and originally in the Word of God, as "typal ideas." Secondly, they are in the elements of the world, where they were produced altogether at the beginning, as in "universal causes." Thirdly, they are in those things which, in the succession of time, are produced by universal causes, for instance in this plant, and in that animal, as in "particular causes." Fourthly, they are in the "seeds" produced from animals and plants. And these again are compared to further particular effects, as the primordial universal causes to the first effects produced.
Reply to Objection 1: These active and passive virtues of natural things, thought not called "virtues" [rationes] by reason of their being in corporeal matter, can nevertheless be so called in respect of their origin, forasmuch as they are the effect of the typal ideas [rationes ideales].
Reply to Objection 2: These active and passive virtues are in certain parts of corporeal things: and when they are employed with local movement for the production of certain results, we speak of the demons as employing seeds.
Reply to Objection 3: The seed of the male is the active principle in the generation of an animal. But that can be called seed also which the female contributes as the passive principle. And thus the word "seed" covers both active and passive principles.
Reply to Objection 4: From the words of Augustine when speaking of these seminal virtues, it is easy to gather that they are also causal virtues, just as seed is a kind of cause: for he says (De Trin. iii, 9) that, "as a mother is pregnant with the unborn offspring, so is the world itself pregnant with the causes of unborn things." Nevertheless, the "typal ideas" can be called "causal virtues," but not, strictly speaking, "seminal virtues," because seed is not a separate principle; and because miracles are not wrought outside the scope of causal virtues. Likewise neither are miracles wrought outside the scope of the passive virtues so implanted in the creature, that the latter can be used to any purpose that God commands. But miracles are said to be wrought outside the scope of the natural active virtues, and the passive potentialities which are ordered to such active virtues, and this is what is meant when we say that they are wrought outside the scope of seminal virtues.

#### Art. 3 - Whether the heavenly bodies are the cause of what is produced in bodies here below?

Objection 1: It would seem that the heavenly bodies are not the cause of what is produced in bodies here below. For Damascene says (De Fide Orth. ii, 7): "We say that they"---namely, the heavenly bodies---"are not the cause of generation or corruption: they are rather signs of storms and atmospheric changes."
Objection 2: Further, for the production of anything, an agent and matter suffice. But in things here below there is passive matter; and there are contrary agents---heat and cold, and the like. Therefore for the production of things here below, there is no need to ascribe causality to the heavenly bodies.
Objection 3: Further, the agent produces its like. Now it is to be observed that everything which is produced here below is produced through the action of heat and cold, moisture and dryness, and other such qualities, which do not exist in heavenly bodies. Therefore the heavenly bodies are not the cause of what is produced here below.
Objection 4: Further, Augustine says (De Civ. Dei v, 6): "Nothing is more corporeal than sex." But sex is not caused by the heavenly bodies: a sign of this is that of twins born under the same constellation, one may be male, the other female. Therefore the heavenly bodies are not the cause of things produced in bodies here below.
On the contrary, Augustine says (De Trin. iii, 4): "Bodies of a grosser and inferior nature are ruled in a certain order by those of a more subtle and powerful nature." And Dionysius (Div. Nom. iv) says that "the light of the sun conduces to the generation of sensible bodies, moves them to life, gives them nourishment, growth, and perfection."
I answer that, Since every multitude proceeds from unity; and since what is immovable is always in the same way of being, whereas what is moved has many ways of being: it must be observed that throughout the whole of nature, all movement proceeds from the immovable. Therefore the more immovable certain things are, the more are they the cause of those things which are most movable. Now the heavenly bodies are of all bodies the most immovable, for they are not moved save locally. Therefore the movements of bodies here below, which are various and multiform, must be referred to the movement of the heavenly bodies, as to their cause.
Reply to Objection 1: These words of Damascene are to be understood as denying that the heavenly bodies are the first cause of generation and corruption here below; for this was affirmed by those who held that the heavenly bodies are gods.
Reply to Objection 2: The active principles of bodies here below are only the active qualities of the elements, such as hot and cold and the like. If therefore the substantial forms of inferior bodies were not diversified save according to accidents of that kind, the principles of which the early natural philosophers held to be the "rare" and the "dense"; there would be no need to suppose some principle above these inferior bodies, for they would be of themselves sufficient to act. But to anyone who considers the matter aright, it is clear that those accidents are merely material dispositions in regard to the substantial forms of natural bodies. Now matter is not of itself sufficient to act. And therefore it is necessary to suppose some active principle above these material dispositions.
This is why the Platonists maintained the existence of separate species, by participation of which the inferior bodies receive their substantial forms. But this does not seem enough. For the separate species, since they are supposed to be immovable, would always have the same mode of being: and consequently there would be no variety in the generation and corruption of inferior bodies: which is clearly false.
Therefore it is necessary, as the Philosopher says (De Gener. ii, 10), to suppose a movable principle, which by reason of its presence or absence causes variety in the generation and corruption of inferior bodies. Such are the heavenly bodies. Consequently whatever generates here below, moves to the production of the species, as the instrument of a heavenly body: thus the Philosopher says (Phys. ii, 2) that "man and the sun generate man."
Reply to Objection 3: The heavenly bodies have not a specific likeness to the bodies here below. Their likeness consists in this, that by reason of their universal power, whatever is generated in inferior bodies, is contained in them. In this way also we say that all things are like God.
Reply to Objection 4: The actions of heavenly bodies are variously received in inferior bodies, according to the various dispositions of matter. Now it happens at times that the matter in the human conception is not wholly disposed to the male sex; wherefore it is formed sometimes into a male, sometimes into a female. Augustine quotes this as an argument against divination by stars: because the effects of the stars are varied even in corporeal things, according to the various dispositions of matter.

#### Art. 4 - Whether the heavenly bodies are the cause of human actions?

Objection 1: It would seem that the heavenly bodies are the cause of human actions. For since the heavenly bodies are moved by spiritual substances, as stated above (Q[110], A[3]), they act by virtue thereof as their instruments. But those spiritual substances are superior to our souls. Therefore it seems that they can cause impressions on our souls, and thereby cause human actions.
Objection 2: Further, every multiform is reducible to a uniform principle. But human actions are various and multiform. Therefore it seems that they are reducible to the uniform movements of heavenly bodies, as to their principles.
Objection 3: Further, astrologers often foretell the truth concerning the outcome of wars, and other human actions, of which the intellect and will are the principles. But they could not do this by means of the heavenly bodies, unless these were the cause of human actions. Therefore the heavenly bodies are the cause of human actions.
On the contrary, Damascene says (De Fide Orth. ii, 7) that "the heavenly bodies are by no means the cause of human actions."
I answer that, The heavenly bodies can directly and of themselves act on bodies, as stated above (A[3]). They can act directly indeed on those powers of the soul which are the acts of corporeal organs, but accidentally: because the acts of such powers must needs be hindered by obstacles in the organs; thus an eye when disturbed cannot see well. Wherefore if the intellect and will were powers affixed to corporeal organs, as some maintained, holding that intellect does not differ from sense; it would follow of necessity that the heavenly bodies are the cause of human choice and action. It would also follow that man is led by natural instinct to his actions, just as other animals, in which there are powers other than those which are affixed to corporeal organs: for whatever is done here below in virtue of the action of heavenly bodies, is done naturally. It would therefore follow that man has no free-will, and that he would have determinate actions, like other natural things. All of which is manifestly false, and contrary to human habit. It must be observed, however, that indirectly and accidentally, the impressions of heavenly bodies can reach the intellect and will, forasmuch, namely, as both intellect and will receive something from the inferior powers which are affixed to corporeal organs. But in this the intellect and will are differently situated. For the intellect, of necessity, receives from the inferior apprehensive powers: wherefore if the imaginative, cogitative, or memorative powers be disturbed, the action of the intellect is, of necessity, disturbed also. The will, on the contrary, does not, of necessity, follow the inclination of the inferior appetite; for although the passions in the irascible and concupiscible have a certain force in inclining the will; nevertheless the will retains the power of following the passions or repressing them. Therefore the impressions of the heavenly bodies, by virtue of which the inferior powers can be changed, has less influence on the will, which is the proximate cause of human actions, than on the intellect.
To maintain therefore that heavenly bodies are the cause of human actions is proper to those who hold that intellect does not differ from sense. Wherefore some of these said that "such is the will of men, as is the day which the father of men and of gods brings on" (Odyssey xviii 135). Since, therefore, it is manifest that intellect and will are not acts of corporeal organs, it is impossible that heavenly bodies be the cause of human actions.
Reply to Objection 1: The spiritual substances, that move the heavenly bodies, do indeed act on corporeal things by means of the heavenly bodies; but they act immediately on the human intellect by enlightening it. On the other hand, they cannot compel the will, as stated above (Q[111], A[2]).
Reply to Objection 2: Just as the multiformity of corporeal movements is reducible to the uniformity of the heavenly movement as to its cause: so the multiformity of actions proceeding from the intellect and the will is reduced to a uniform principle which is the Divine intellect and will.
Reply to Objection 3: The majority of men follow their passions, which are movements of the sensitive appetite, in which movements of the heavenly bodies can cooperate: but few are wise enough to resist these passions. Consequently astrologers are able to foretell the truth in the majority of cases, especially in a general way. But not in particular cases; for nothing prevents man resisting his passions by his free-will. Wherefore the astrologers themselves are wont to say that "the wise man is stronger than the stars" [*Ptolemy, Centiloquium, prop. 5], forasmuch as, to wit, he conquers his passions.

#### Art. 5 - Whether heavenly bodies can act on the demons?

Objection 1: It would seem that heavenly bodies can act on the demons. For the demons, according to certain phases of the moon, can harass men, who on that account are called lunatics, as appears from Mat. 4:24 and 17:14. But this would not be if they were not subject to the heavenly bodies. Therefore the demons are subject to them.
Objection 2: Further, necromancers observe certain constellations in order to invoke the demons. But these would not be invoked through the heavenly bodies unless they were subject to them. Therefore they are subject to them.
Objection 3: Further, heavenly bodies are more powerful than inferior bodies. But the demons are confined to certain inferior bodies, namely, "herbs, stones, animals, and to certain sounds and words, forms and figures," as Porphyry says, quoted by Augustine (De Civ. Dei x, 11). Much more therefore are the demons subject to the action of heavenly bodies.
On the contrary, The demons are superior in the order of nature, to the heavenly bodies. But the "agent is superior to the patient," as Augustine says (Gen. ad lit. xii, 16). Therefore the demons are not subject to the action of heavenly bodies.
I answer that, There have been three opinions about the demons. In the first place the Peripatetics denied the existence of demons; and held that what is ascribed to the demons, according to the necromantic art, is effected by the power of the heavenly bodies. This is what Augustine (De Civ. Dei x, 11) relates as having been held by Porphyry, namely, that "on earth men fabricate certain powers useful in producing certain effects of the stars." But this opinion is manifestly false. For we know by experience that many things are done by demons, for which the power of heavenly bodies would in no way suffice: for instance, that a man in a state of delirium should speak an unknown tongue, recite poetry and authors of whom he has no previous knowledge; that necromancers make statues to speak and move, and other like things.
For this reason the Platonists were led to hold that demons are "animals with an aerial body and a passive soul," as Apuleius says, quoted by Augustine (De Civ. Dei viii, 16). And this is the second of the opinions mentioned above: according to which it could be said that demons are subject to heavenly bodies in the same way as we have said man is subject thereto (A[4]). But this opinion is proved to be false from what we have said above (Q[51], A[1]): for we hold that demons are spiritual substances not united to bodies. Hence it is clear that they are subject to the action of heavenly bodies neither essentially nor accidentally, neither directly nor indirectly.
Reply to Objection 1: That demons harass men, according to certain phases of the moon, happens in two ways. Firstly, they do so in order to "defame God's creature," namely, the moon; as Jerome (In Matt. iv, 24) and Chrysostom (Hom. lvii in Matt.) say. Secondly, because as they are unable to effect anything save by means of the natural forces, as stated above (Q[114], A[4], ad 2) they take into account the aptitude of bodies for the intended result. Now it is manifest that "the brain is the most moist of all the parts of the body," as Aristotle says [*De Part. Animal. ii, 7: De Sens. et Sensato ii: De Somn. et Vigil. iii]: wherefore it is the most subject to the action of the moon, the property of which is to move what is moist. And it is precisely in the brain that animal forces culminate: wherefore the demons, according to certain phases of the moon, disturb man's imagination, when they observe that the brain is thereto disposed.
Reply to Objection 2: Demons when summoned through certain constellations, come for two reasons. Firstly, in order to lead man into the error of believing that there is some Divine power in the stars. Secondly, because they consider that under certain constellations corporeal matter is better disposed for the result for which they are summoned.
Reply to Objection 3: As Augustine says (De Civ. Dei xxi, 6), the "demons are enticed through various kinds of stones, herbs, trees, animals, songs, rites, not as an animal is enticed by food, but as a spirit by signs"; that is to say, forasmuch as these things are offered to them in token of the honor due to God, of which they are covetous.

#### Art. 6 - Whether heavenly bodies impose necessity on things subject to their action?

Objection 1: It would seem that heavenly bodies impose necessity on things subject to their action. For given a sufficient cause, the effect follows of necessity. But heavenly bodies are a sufficient cause of their effects. Since, therefore, heavenly bodies, with their movements and dispositions, are necessary beings; it seems that their effects follow of necessity.
Objection 2: Further, an agent's effect results of necessity in matter, when the power of the agent is such that it can subject the matter to itself entirely. But the entire matter of inferior bodies is subject to the power of heavenly bodies, since this is a higher power than theirs. Therefore the effect of the heavenly bodies is of necessity received in corporeal matter.
Objection 3: Further, if the effect of the heavenly body does not follow of necessity, this is due to some hindering cause. But any corporeal cause, that might possibly hinder the effect of a heavenly body, must of necessity be reducible to some heavenly principle: since the heavenly bodies are the causes of all that takes place here below. Therefore, since also that heavenly principle is necessary, it follows that the effect of the heavenly body is necessarily hindered. Consequently it would follow that all that takes place here below happens of necessity.
On the contrary, The Philosopher says (De Somn. et Vigil. [*De Divin. per Somn. ii]): "It is not incongruous that many of the signs observed in bodies, of occurrences in the heavens, such as rain and wind, should not be fulfilled." Therefore not all the effects of heavenly bodies take place of necessity.
I answer that, This question is partly solved by what was said above (A[4]); and in part presents some difficulty. For it was shown that although the action of heavenly bodies produces certain inclinations in corporeal nature, the will nevertheless does not of necessity follow these inclinations. Therefore there is nothing to prevent the effect of heavenly bodies being hindered by the action of the will, not only in man himself, but also in other things to which human action extends.
But in natural things there is no such principle, endowed with freedom to follow or not to follow the impressions produced by heavenly agents. Wherefore it seems that in such things at least, everything happens of necessity; according to the reasoning of some of the ancients who supposing that everything that is, has a cause; and that, given the cause, the effect follows of necessity; concluded that all things happen of necessity. This opinion is refuted by Aristotle (Metaph. vi, Did. v, 3) as to this double supposition.
For in the first place it is not true that, given any cause whatever, the effect must follow of necessity. For some causes are so ordered to their effects, as to produce them, not of necessity, but in the majority of cases, and in the minority to fail in producing them. But that such cases do fail in the minority of cases is due to some hindering cause; consequently the above-mentioned difficulty seems not to be avoided, since the cause in question is hindered of necessity.
Therefore we must say, in the second place, that everything that is a being "per se," has a cause; but what is accidentally, has not a cause, because it is not truly a being, since it is not truly one. For (that a thing is) "white" has a cause, likewise (that a man is) "musical" has not a cause, but (that a being is) "white-musical" has not a cause, because it is not truly a being, nor truly one. Now it is manifest that a cause which hinders the action of a cause so ordered to its effect as to produce it in the majority of cases, clashes sometimes with this cause by accident: and the clashing of these two causes, inasmuch as it is accidental, has no cause. Consequently what results from this clashing of causes is not to be reduced to a further pre-existing cause, from which it follows of necessity. For instance, that some terrestrial body take fire in the higher regions of the air and fall to the earth, is caused by some heavenly power: again, that there be on the surface of the earth some combustible matter, is reducible to some heavenly principle. But that the burning body should alight on this matter and set fire to it, is not caused by a heavenly body, but is accidental. Consequently not all the effects of heavenly bodies result of necessity.
Reply to Objection 1: The heavenly bodies are causes of effects that take place here below, through the means of particular inferior causes, which can fail in their effects in the minority of cases.
Reply to Objection 2: The power of a heavenly body is not infinite. Wherefore it requires a determinate disposition in matter, both as to local distance and as to other conditions, in order to produce its effect. Therefore as local distance hinders the effect of a heavenly body (for the sun has not the same effect in heat in Dacia as in Ethiopia); so the grossness of matter, its low or high temperature or other such disposition, can hinder the effect of a heavenly body.
Reply to Objection 3: Although the cause that hinders the effect of another cause can be reduced to a heavenly body as its cause; nevertheless the clashing of two causes, being accidental, is not reduced to the causality of a heavenly body, as stated above.