draw it: And though he should be convinced that his understanding has no
part in the operation, he would nevertheless continue in the same course
of thinking. There is some other principle which determines him to form
such a conclusion.

36. This principle is Custom or Habit. For wherever the repetition of
any particular act or operation produces a propensity to renew the same
act or operation, without being impelled by any reasoning or process of
the understanding, we always say, that this propensity is the effect of
_Custom_. By employing that word, we pretend not to have given the
ultimate reason of such a propensity. We only point out a principle of
human nature, which is universally acknowledged, and which is well known
by its effects. Perhaps we can push our enquiries no farther, or pretend
to give the cause of this cause; but must rest contented with it as the
ultimate principle, which we can assign, of all our conclusions from
experience. It is sufficient satisfaction, that we can go so far,
without repining at the narrowness of our faculties because they will
carry us no farther. And it is certain we here advance a very
intelligible proposition at least, if not a true one, when we assert
that, after the constant conjunction of two objects--heat and flame, for
instance, weight and solidity--we are determined by custom alone to
expect the one from the appearance of the other. This hypothesis seems
even the only one which explains the difficulty, why we draw, from a
thousand instances, an inference which we are not able to draw from one
instance, that is, in no respect, different from them. Reason is
incapable of any such variation. The conclusions which it draws from
considering one circle are the same which it would form upon surveying
all the circles in the universe. But no man, having seen only one body
move after being impelled by another, could infer that every other body
will move after a like impulse. All inferences from experience,