contributes to increase our knowledge; but it is the greater energy and
activity of the power of volition (as explained in the former Sections of
this work) that marks mankind, and has given him the empire of the world.

There is a criterion by which we may distinguish our voluntary acts or
thoughts from those that are excited by our sensations: "The former are
always employed about the _means_ to acquire pleasureable objects, or to
avoid painful ones: while the latter are employed about the _possession_ of
those that are already in our power."

If we turn our eyes upon the fabric of our fellow animals, we find they are
supported with bones, covered with skins, moved by muscles; that they
possess the same senses, acknowledge the same appetites, and are nourished
by the same aliment with ourselves; and we should hence conclude from the
strongest analogy, that their internal faculties were also in some measure
similar to our own.

Mr. Locke indeed published an opinion, that other animals possessed no
abstract or general ideas, and thought this circumstance was the barrier
between the brute and the human world. But these abstracted ideas have been
since demonstrated by Bishop Berkley, and allowed by Mr. Hume, to have no
existence in nature, not even in the mind of their inventor, and we are
hence necessitated to look for some other mark of distinction.

The ideas and actions of brutes, like those of children, are almost
perpetually produced by their present pleasures, or their present pains;
and, except in the few instances that have been mentioned in this Section,
they seldom busy themselves about the _means_ of procuring future bliss, or
of avoiding future misery.