on that side, and you'll see the passion clear every moment, 'till it changes insensibly into hope; which again runs, after the same manner, by slow degrees, into joy, as you encrease that part of the composition by the encrease of the probability. Are not these as plain proofs, that the passions of fear and hope are mixtures of grief and joy, as in optics 'tis a proof, that a colour'd ray of the sun passing thro' a prism, is a composition of two others, when, as you diminish or encrease the quantity of either, you find it prevail proportionably more or less in the composition? I am sure neither natural nor moral philosophy admits of stronger proofs.
Probability is of two kinds, either when the object is really in itself uncertain, and to be determin'd by chance; or when, tho' the object be already certain, yet 'tis uncertain to our judgment, which finds a number of proofs on each side of the question. Both these kinds of probabilities cause fear and hope; which can only proceed from that property, in which they agree, viz. the uncertainty and fluctuation they bestow on the imagination by that contrariety of views, which is common to both.
'Tis a probable good or evil, that commonly produces hope or fear; because probability, being a wavering and inconstant method of surveying an object, causes naturally a like mixture and uncertainty of passion. But we may observe, that wherever from other causes this mixture can be produc'd, the passions of fear and hope will arise, even tho' there be no probability; which must be allow'd to be a convincing proof of the present hypothesis.
We find that an evil, barely conceiv'd as possible, does sometimes produce fear; especially if the evil be very great. A man cannot think of excessive pains and tortures without trembling, if he be in the least danger of suffering them. The smallness of the probability is compensated by the greatness of the evil; and the sensation is equally lively, as if the evil were more probable. One view or glimpse of the former, has the same effect as several of the latter.
