e joy continually diminishes, into pure
grief. After you have brought it to this situation, diminish the
grief, after the same manner that you encreased it; by diminishing the
probability on that side, and you'll see the passion clear every moment,
until 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 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. One view or glimpse
of the former, has the same effect as several of the latter.

But they are not only possible evils, that cause fear, but even
some allowed to be impossible; as when we tremble on the brink of a
precipice, though we know ourselves to be in perfect securi