(6) Now to our second point of study. Every agent intends good, and better so far as it can (Chap. III). But good and better do not have place in the same way in a whole and in its parts. In the whole the good is the entire effect arising out of the order and composition of the parts: hence it is better for the whole that there should be inequality among the parts, without which inequality the order and perfection of the whole cannot be, than that all the parts should be equal, every one of them attaining to the rank of the noblest part. And yet, considered by itself, every part of lower rank would be better if it were in the rank of some superior part. Thus in the human body the foot would be a more dignified part of man if it had the beauty and power of the eye; but the whole body would be worse off for lacking the office of the foot. The scope and aim therefore of the particular agent is not the same as that of the universal agent. The particular agent tends to the good of the part absolutely, and makes the best of it that it can; but the universal agent tends to the good of the whole: hence a defect may be beside the intention of the particular agent, but according to the intention of the universal agent. It is the intention of the particular agent that its effect should be perfect to the utmost possible in its kind: but it is the intention of the universal agent that this effect be carried to a certain degree of perfection and no further. Now between the parts of the universe the first apparent difference is that of contingent and necessary. Beings of a higher order are necessary and indestructible and unchangeable: from which condition beings fall away, the lower the rank in which they are placed; so that the lowest beings suffer destruction in their being and change in their constitution, and produce their effects, not necessarily, but contingently. Every agent therefore that is part of the universe endeavours, so far as it can, to abide in its being and natural constitution, and to establish its effect: but God, the governor of the universe, intends that of the effects which take place in it one be established as of necessity, another as of contingency; and with this view He applies different causes to them, necessary causes to these effects, contingent causes to those. It falls under divine providence therefore, not only that this effect be, but also that this effect be necessarily, that other contingently. Thus, of things subject to divine providence, some are necessary, and others contingent, not all necessary.
Hence it is clear that this conditional proposition is true: 'If God has foreseen this thing in the future, it will be.' But it will be as God has provided that it shall be; and supposing that He has provided that it shall be contingently, it follows infallibly that it will be contingently, and not necessarily.
Cicero (De divinatione ii, 8) has this argument: 'If all things are foreseen by God, the order of causes is certain; but if so, all things happen by fate, nothing is left in our power, and there is no such thing as free will.' A frivolous argument, for since not only effects are subject to divine providence, but also causes, and modes of being, it follows that though all things happen by divine providence, some things are so foreseen by God as that they are done freely by us.
Nor can the defectibility of secondary causes, by means of which the effects of providence are produced, take away the certainty of divine providence: for since God works in all things, it belongs to His providence sometimes to allow defectible causes to fail, and sometimes to keep them from failing.
The Philosopher shows * that if every effect has a proper cause (causam per se), every future event may be reduced to some present or past cause. Thus if the question is put concerning any one, whether he is to be slain by robbers, that effect proceeds from a cause, his meeting with robbers; and that effect again is preceded by another cause, his going out of his house; and that again by another, his wanting to find water; the preceding cause to which is thirst, and this is caused by eating salt meat, which he either is doing or has done. If then, positing the cause, the effect must be posited of necessity, he must necessarily be thirsty, if he eats salt meat; and he must necessarily will to seek water, if he is thirsty; and be must necessarily go out of the house, if he wills to seek water; and the robbers must necessarily come across him, if he goes out of the house; and if they come across him, he must be killed. Therefore from first to last it is necessary for this man eating salt meat to be killed by robbers.* The philosopher concludes that it is not true that, positing the cause, the effect must be posited, because there are some causes that may fail.* Nor again is it true that every effect has a proper cause: for any accidental effect, e.g., of this man wishing to look for water and falling in with robbers, has no cause.*
3.93 : Of Fate, whether there be such a thing, and if so, what it is
3.95, 96 : That the Immutability of Divine Providence does not bar the Utility of Prayer