then, the processes which bring these cases within the
same category with the rest, require that we should
assume the universality of the very law which they do
not at first sight appear to exemplify, is not this a
real _petitio principii_? Can we prove a proposition by
an argument which takes it for granted? And, if not so
proved, on what evidence does it rest?

"For this difficulty, which I have purposely stated in
the strongest terms it would admit of, the school of
metaphysicians, who have long predominated in this
country, find a ready salvo. They affirm that the
universality of causation is a truth which we cannot
help believing; that the belief in it is an instinct,
one of the laws of our believing faculty. As the proof
of this they say, and they have nothing else to say,
that every body _does_ believe it; and they number it
among the propositions, rather numerous in their
catalogue, which may be logically argued against, and
perhaps cannot be logically proved, but which are of
higher authority than logic, and which even he who
denies in speculation, shows by his habitual practice
that his arguments make no impression on himself.

"I have no intention of entering into the merits of this
question, as a problem of transcendental metaphysics.
But I must renew my protest against adducing, as
evidence of the truth of a fact in external nature, any
necessity which the human mind may be conceived to be
under of believing it. It is the business of human
intellect to adapt itself to the realities of things,
and not to measure those realities by its own capacities
of comprehension. The same quality which fits mankind
for the offices and purposes of their own little life,
the tendency of their belief to follow their experience,
incapacitates them for judging of what lies beyond. Not
only what man can know, but what he can conceive,
depends upon what he has experienced. Whatever forms a
part of all his experience, forms a part also of all his
conceptions, and appears to him universal and necessary,
though really, for aught he knows, having no existence
beyond certain narrow limits. The habit, however, of
philosophical analysis, of which it is the surest effect
to enable the mind to command, instead of being
commanded by, the laws of the merely pas