y on human
creatures, but also on the Deity himself: All these systems concur in
the opinion, that morality, like truth, is discerned merely by ideas,
and by their juxta-position and comparison. In order, therefore, to
judge of these systems, we need only consider, whether it be possible,
from reason alone, to distinguish betwixt moral good and evil, or
whether there must concur some other principles to enable us to make
that distinction.

If morality had naturally no influence on human passions and actions,
it were in vain to take such pains to inculcate it; and nothing would be
more fruitless than that multitude of rules and precepts, with which all
moralists abound. Philosophy is commonly divided into speculative and
practical; and as morality is always comprehended under the latter
division, it is supposed to influence our passions and actions, and to
go beyond the calm and indolent judgments of the understanding. And this
is confirmed by common experience, which informs us, that men are often
governed by their duties, and are detered from some actions by the
opinion of injustice, and impelled to others by that of obligation.

Since morals, therefore, have an influence on the actions and
affections, it follows, that they cannot be derived from reason; and
that because reason alone, as we have already proved, can never have any
such influence. Morals excite passions, and produce or prevent actions.
Reason of itself is utterly impotent in this particular. The rules of
morality therefore, are not conclusions of our reason.

No one, I believe, will deny the justness of this inference; nor is
there any other means of evading it, than by denying that principle,
on which it is founded. As long as it is allowed, that reason has no
influence on our passions and action, it is in vain to pretend,
that morality is discovered only by a deduction of reason. An active
principle can never be founded on an inactive; and if reason be inactive
in itself, it must remain so in all its shapes and appearances, whether
it exerts itself in natural or moral subjects, whether it considers the
powers of external bodies, or the actions of rational beings.

It would be tedious to repeat all the arguments, by which I have proved
[Book II. Part III. Sect 3.], that reason is perfectly inert, and can
never either prevent or produce any action or affection, it will be easy
to recollect what has been said upon that subject. I shall only recall
on