Are not these as plain proofs, that the passions of fear and hope are mixtures of grief and joy, as in optics it is a proof, that a coloured ray of the sun passing through 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 determined by chance; or when, though the object be already certain, yet it is 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.
It is a probable good or evil, that commonly produces hope or fear; because probability, being a wavering and unconstant 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 produced, the passions of fear and hope will arise, even though there be no probability; which must be allowed to be a convincing proof of the present hypothesis.

We find that an evil, barely conceived 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.