Page:Four Dissertations - David Hume (1757).djvu/144

 into hope; which again runs, 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 it is a proof, that a coloured 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?

5. is of two kinds; either when the object is itself uncertain, and to be determined by chance; or when, tho' the object be already certain, yet is it uncertain to our judgment, which finds a number of proofs or presumptions on each side of the question. Both these kinds of probability cause fear and hope; which must proceed from that property, in which they agree; to wit, the uncertainty and fluctuation which they bestow on the passion, by that contrariety of views, which is common to both.