Summa contra Gentiles3.74 Chapter LXXIV. That divine providence does not exclude chance or luck

It is also evident from what has been said that divine providence does not remove from the world chance and luck.

Chance and luck are said of things that happen seldom. If nothing happened seldom, all things would happen of necessity; because those things that happen more frequently than not, differ from necessary things in this alone, that they may possibly fail in a few instances. Now it would be inconsistent with divine providence if all things happened of necessity, as we proved above.’ Therefore it would also be inconsistent with divine providence if there were no luck or chance in the world.

Again. It would be contrary to the nature of providence if things subject to providence were not to act for an end, since it is the part of providence to direct all things to their universe, were there nothing corruptible, nor any defectible power, as we proved above.” Now it is owing to the fact that an agent acting for the sake of some end fails to attain that end, that certain things happen by chance. Therefore it would be contrary to the nature of providence, and to the perfection of the world, if nothing happened by chance. Besides. The number and variety of causes result from the ordering of divine providence and disposition. Now given a diversity of causes, it must happen sometimes that one concurs with another, so that one is either hindered or assisted in producing its effect. Now chance occurrences are due to the concurrence of two or more causes, through some end which was not intended ensuing from the concurrence of some cause: for instance, the finding of his debtor by one who went to market to buy something, resulted from the debtor also going to market. Therefore it is not incompatible with divine providence that there be luck and chance in things.

Moreover. That which is not, cannot be the cause of any thing, wherefore a thing must stand in relation to being a cause, in the same way as to being. Wherefore the diversity of order in causes must be in keeping with diversity of order among things. Now it belongs to the perfection of things that not only there be some that are beings er se, but that there be also some accidental beings. Because things which have not their ultimate perfection in their substance, must needs acquire some perfection by means of accidents, which accidents will be all the more numerous, as the things themselves are more distant from God’s simplicity. Now if asubject has many accidents it follows that it is a being accidentally: since subject and accident, or again two accidents in one subject, are one accidentally, for instance a white man, and a musical white thing. Therefore the perfection of the world requires that there should be also accidental causes. But that which results accidentally from a cause, is said to occur by chance or by luck. Therefore it is not inconsistent with providence that certain things happen by chance or luck.

Further. It belongs to the order of divine providence that there be order and degrees among causes. The higher a cause is above its effect, the greater its power, so that its—causality extends to a greater number of things. But the intention of a natural cause never extends further than its power: for such an intention would be in vain. Consequently the intention of an individual cause cannot possibly extend to all possible contingencies. Now it is through things happening beside the intention of the agent that things occur by chance or luck. Therefore the order of divine providence requires the presence of luck and chance in the world.

Hence it is said (Eccles. ix. 11): J saw that... the race is not to the swift, etc., but time and chance in all, namely here below.