This is enormously long, and I was tempted to cut some of the less important material, but decided to keep it all because the progression would be damaged too much by its removal. The main point of this, roughly, is that, given the “system” set up by God, some things must exist necessarily. Physicists are well advised to read this, for it proves an understanding of being and necessity is fundamentally important for their field. Stick to the end with paragraph 15, too, for wisdom about final causes.
1 Now though all things depend on God’s will as their first cause, which is not necessitated in operating except by the supposition of His purpose, nevertheless absolute necessity is not therefore excluded from things, so that we be obliged to assert that all things are contingent:–which some one might think to be the case, for the reason that they have arisen from their cause, not of absolute necessity: since in things a contingent effect is wont to be one that does not necessarily result from a cause. Because there are some created things which it is simply and absolutely necessary must be.
2 For it is simply and absolutely necessary that those things be in which there is no possibility of not being. Now some things are so brought by God into being, that there is in their nature a potentiality to non-being. This happens through their matter being in potentiality to another form. Wherefore those things, wherein either there is no matter, or, if there is, it has not the possibility of receiving another form, have not a potentiality to non-being. Hence it is simply and absolutely necessary for them to be.
3 If, however, it be said that things which are from nothing, so far as they are concerned, tend to nothing, and that in consequence there is in all creatures a potentiality to nonbeing:–it is clear that this does not follow. For created things are said to tend to nothing in the same sense as they are from nothing: and this is not otherwise than according to the power of the agent. Wherefore in created things there is not a potentiality to non-being: but there is in the Creator the power to give them being or to cease pouring forth being into them: since He works in producing things, not by a necessity of His nature, but by His will, as we have proved.
4 Again. Since created things come into being through the divine will, it follows that they are such as God willed them to be. Now the fact that God is said to have brought things into being by His will, and not of necessity, does not exclude His having willed certain things to be which are of necessity, and others which are contingently, so that there may be an ordinate diversity in things. Nothing, therefore, prevents certain things produced by the divine will being necessary.
5 Further. It belongs to God’s perfection that He bestowed His likeness on created things, except as regards those things with which created being is incompatible: since it belongs to a perfect agent to produce its like as far as possible. Now to be simply necessary is not incompatible with the notion of created being: for nothing prevents a thing being necessary which nevertheless has a cause of its necessity, for instance, the conclusions of demonstrations. Therefore nothing prevents a certain thing being so produced by God, that nevertheless it is simply necessary for it to be: in fact, this is a proof of the divine perfection.
Notes The key passages thus far (from 1) “there are some created things which it is simply and absolutely necessary must be” and (from 5) “nothing prevents a thing being necessary which nevertheless has a cause of its necessity”. And the example to the latter is lovely, “the conclusions of demonstrations”, which has in itself the proof of itself. Sweet.
6 Moreover. The further distant a thing is from that which is being of itself, namely God, the nearer is it to non-being. Wherefore the nearer a thing is to God, the further is it removed from non-being. Now things that already are, are near to non-being through having a potentiality to non-being. Consequently, those things which are nearest to God, and for that reason most remote from nonbeing, must be such that there is no potentiality to nonbeing in them, so that the order in things be complete: and the like are necessary absolutely. Therefore some created things have being necessarily.
7 Accordingly it must be observed that if the universe of created beings be considered as coming from their first principle, we find that they depend on the will, not on a necessity of their principle, except on a necessity of supposition, as already stated. If, however, they be considered in relation to their proximate principles, they are found to have absolute necessity. For nothing prevents certain principles being produced, not of necessity, and yet, these being supposed, such and such an effect follows of necessity: thus the death of this animal has absolute necessity from the very fact that it is composed of contraries, although it was not absolutely necessary for it to be composed of contraries. In like manner that such and such natures were produced by God, was voluntary: and yet, once they are so constituted, something results or happens that has absolute necessity.
8 In created things, however, necessity is to be taken in various ways in relation to various causes. For since a thing cannot be without its essential principles which are matter and form, that which belongs to a thing by reason of its essential principles must needs have absolute necessity in all things.
Notes Pay attention to this one (8).
9 Now from these principles, in so far as they are principles of being, a threefold absolute necessity is found in things.
First in relation to the being of the thing of which they are the principles. And since matter, as regards what it is, is being in potentiality; and since what can be, can also not be; in relation to their matter certain things are necessarily corruptible; for instance, an animal, through being composed of contraries, and fire, through its matter being susceptive of contraries. But form, as regards what it is, is act, and by it things exist actually. Wherefore from it there results necessity in some things.
This happens either because those things are forms without matter,–and thus there is no potentiality to non-being in them, but by their forms they are always in the act of being, as in the case of separate substances–or because their forms are so perfect as to equal the whole potentiality of their matter, wherefore there remains no potentiality to another form, nor, in consequence, to non-being, as in the case of heavenly bodies.
But in those things wherein the form does not fulfil the whole potentiality of matter, there still remains a potentiality to another form. Wherefore in them there is not necessity of being, but the act of being is, in them, the result of form overcoming matter, as in the case of the elements and things composed of them. Because the form of an element does not reach matter in its whole potentiality: for matter does not receive the form of one element, except by being subjected to the one of two contraries. While the form of a mixed body reaches matter as disposed by a determinate mode of mixture. Now there must be one same subject of contraries, and of all intermediaries resulting from the mixture of the extremes. Wherefore it is evident that all things which either have contraries, or are composed of contraries, are corruptible. And things which are not so, are everlasting: unless they be corrupted accidentally, as forms which are not subsistent, and have being through being in matter.
10 In another way there is absolute necessity in things from their essential principles, by relation to the parts of their matter or form, if it happens that in certain things these principles are not simple. For since the proper matter of man is a mixed body, with a certain temperament and endowed with organs, it is absolutely necessary that a man should have in himself each of the elements, humours, and principal organs. Likewise if man is a rational mortal animal, and this is the nature or form of a man, it is necessary for him to be both animal and rational.
Notes You have to be what you are, or you aren’t what you claim to be. (Humorous; vaguely.)
11 Thirdly, there is absolute necessity in things through the relations of their essential principles to the properties consequent upon their matter or form: thus it is necessary that a saw be hard, since it is of iron, and that a man be capable of learning.
12 But necessity of the agent may regard either the action itself, or the consequent effect. The former kind of necessity is like the necessity of an accident which it owes to the essential principles. For just as other accidents result from the necessity of essential principles, so does action from the necessity of the form whereby the agent actually is: since it acts so far as it is actual.
Yet this happens differently in the action which remains in the agent, such as to understand and to will, and in the action which passes into something else, such as to heat. For in the former kind of action, the form by which the agent becomes actual causes necessity in the action itself, since for its being nothing extrinsic is required as term of the action. Because when the sense is made actual by the sensible species, it is necessary for it to perceive, and in like manner, when the intellect is made actual by the intelligible species. But in the second kind of action, necessity of action results from the form, as regards the power to act: for if fire is hot, it is necessary that it have the power to heat, although it is not necessary that it heat, since it may be hindered by something extrinsic. Nor does it affect the point at issue, whether by its form one agent be sufficient alone for the action, or whether it be necessary to have an assemblage of many agents in order to do the one action; for instance many men to row a boat: since all are as one agent, who is made actual by their being united together in one action.
13 The necessity which results from an efficient or moving cause in the effect or thing moved, depends not only on the agent, but also on a condition of the thing moved and of the recipient of the agent’s action, which recipient either is nowise in potentiality to receive the effect of such an action,–as wool to be made into a saw,–or else its potentiality is hindered by contrary agents, or by contrary dispositions inherent to the movable, or by contrary forms, offering an obstacle that is stronger than the power of the agent in acting; thus iron is not melted by a feeble heat.
14 Hence, in order that the effect follow, it is necessary that there be in the patient potentiality to receive, and in the agent conquest of the patient, so that it be able to transform it to a contrary disposition. And if the effect, resulting in the patient through its conquest by the agent, be contrary to the natural disposition of the patient, there will be necessity of violence, as when a stone is thrown upwards.
But if it be not contrary to the natural disposition of the subject, there will be necessity not of violence, but of the natural order, as in the movement of the heavens, which results from an extrinsic active principle, and nevertheless is not contrary to the natural disposition of the movable subject, wherefore it is not a violent but a natural movement. It is the same in the alteration of lower bodies by the heavenly bodies: for there is a natural inclination in the lower bodies to receive the influence of the higher bodies. It is also thus in the generation of the elements: since the form to be introduced by generation is not contrary to primary matter, which is the subject of generation, although it is contrary to the form to be cast aside, because matter under a contrary form is not the subject of generation.
Accordingly it is clear from what we have said that the necessity resulting from an efficient cause depends, in some things, on the disposition of the agent alone, but in others on the disposition of both agent and patient. If then this disposition, by reason of which the effect follows of necessity, be absolutely necessary in both agent and patient, there will be absolute necessity in the efficient cause: as in those things which act necessarily and always. On the other hand, if it be not absolutely necessary but may be removed, no necessity will result from the efficient cause except on the supposition that both have the disposition required for action: as, for instance, in those things which are sometimes hindered in their operation either through defective power, or through the violence of a contrary: wherefore they do not act always and necessarily, but in the majority of cases.
15 From a final cause there results necessity in things in two ways. In one way, forasmuch as it is first in the intention of the agent. In this respect necessity results from the end in the same way as from the agent: since the agent acts in so far as it intends the end, both in natural and in voluntary actions. For in natural things, the intention of the end belongs to the agent according to the latter’s form, whereby the end is becoming to it: wherefore the natural thing must needs tend to the end according to the virtue of its form: thus a heavy body tends towards the centre according to the measure of its gravity. And in voluntary matters, the will inclines to act for the sake of an end forasmuch as it intends that end: although it is not always inclined to do this or that, which are on account of the end, as much as it desires the end, when the end can be obtained not by this or that alone, but in several ways.
16 In another way necessity results from the end according as this is posterior in being. This is not absolute but conditional necessity: thus we say that it will be necessary for a saw to be made of iron, if it is to do the work of a saw.
Notes Whew! It’s this last paragraph which wraps it all up and is one of the more important ones, especially for science. Here then is the chapter is brief: Saws are contingent, meaning they do not have to be, but the form of a saw is not contingent, and if a saw is to exist, it must necessarily have certain properties.