change of state or impression. An unvarying action on any of our senses
is the same as no action at all. An even temperature, such as that
enjoyed by the fishes in the tropical seas, leaves the mind an entire
blank as regards heat and cold. We can neither feel nor know without
recognising two distinct states. Hence all knowledge is double, or is
the knowledge of contrasts or opposites: heavy is relative to light; up
supposes down; being awake implies the state of sleep.

The applications of the law in the sphere of emotion are chiefly
contemplated in what follows. Pleasure and pain are never absolute
states; they have reference always to the previous condition. Until we
know what that has been in any case, we cannot pronounce upon the
efficacy of a present stimulation. We see a person reposing, apparently
in luxurious ease; if the state has been immediately consequent upon a
protracted and severe exertion, we are right in calling it highly
pleasurable. Under other circumstances, it might be quite the reverse.

There is an offshoot or modification of the principle, arising out of
the operation of habit. Impressions made upon us are greatest when they
are absolutely new: after repetition they all lose something of their
power; although, by remission and alternative, the causes of pleasure
and pain have still a very considerable efficacy. Many of the
consequences of this great fact are sufficiently acknowledged, or, if
they are not, it is from other causes than our ignorance. The weakness
is moral, rather than intellectual, that makes us expect that the first
flush of a great pleasure, a newly-attained joy or success, will
continue unabated. The poor man, probably, does not overrate the
gratification of newly-attained wealth; what he fails to allow for is
the deadening effect of an unbroken experience of ease and plenty. The
author of "Romola" says of the hero and the heroine, in the early