T 2.1.10.6

Now if we compare these two cases, that of a person, who has very strong motives of interest or safety to forbear any action, and that of another, who lies under no such obligation, we shall find, according to the philosophy explain'd in the foregoing book, that the only known difference betwixt them lies in this, that in the former case we conclude from past experience, that the person never will perform that action, and in the latter, that he possibly or probably will perform it. |Nothing is more fluctuating and inconstant on many occasions, than the will of man; nor is there any thing but strong motives, which can give us an absolute certainty in pronouncing concerning any of his future actions. When we see a person free from these motives, we suppose a possibility either of his acting or forbearing; and tho' in general we may conclude him to be determin'd by motives and causes, yet this removes not the uncertainty of our judgment concerning these causes, nor the influence of that uncertainty on the passions. Since therefore we ascribe a power of performing an action to every one, who has no very powerful motive to forbear it, and refuse it to such as have; it may justly be concluded, that power has always a reference to its exercise, either actual or probable, and that we consider a person as endow'd with any ability when we find from past experience, that 'tis probable, or at least possible he may exert it. And indeed, as our passions always regard the real existence of objects, and we always judge of this reality from past instances; nothing can be more likely of itself, without any farther reasoning, than that power consists in the possibility or probability of any action, as discover'd by experience and the practice of the world.