Secondly, We may call to remembrance the preceding system of the passions, in order to remark a still more considerable difference among our pains and pleasures.  Pride and humility, love and hatred are excited, when there is any thing presented to us, that both bears a relation to the object of the passion, and produces a separate sensation related to the sensation of the passion.  Now virtue and vice are attended with these circumstances.  They must necessarily be placed either in ourselves or others, and excite either pleasure or uneasiness; and therefore must give rise to one of these four passions; which clearly distinguishes them from the pleasure and pain arising from inanimate objects, that often bear no relation to us:  And this is, perhaps, the most considerable effect that virtue and vice have upon the human mind.

It may now be asked in general, concerning this pain or pleasure, that distinguishes moral good and evil, from what principles is it derived, and whence does it arise in the human mind?  To this I reply, first, that it is absurd to imagine, that in every particular instance, these sentiments are produced by an original quality and primary constitution.  For as the number of our duties is, in a manner, infinite, it is impossible that our original instincts should extend to each of them, and from our very first infancy impress on the human mind all that multitude of precepts, which are contained in the compleatest system of ethics.  Such a method of proceeding is not conformable to the usual maxims, by which nature is conducted, where a few principles produce all that variety we observe in the universe, and every thing is carryed on in the easiest and most simple manner.  It is necessary, therefore, to abridge these primary impulses, and find some more general principles, upon which all our notions of morals are founded.

But in the second place, should it be asked, Whether we ought to search for these principles in nature, or whether we must look for them in some other origin?  I would reply, that our answer to this question depends upon the definition of the word, Nature, than which there is none more ambiguous and equivocal.  If nature be opposed to miracles, not only the distinction betwixt vice and virtue is natural, but also every event, which has ever happened in the world, excepting those miracles, on which our religion is founded. In saying, then, that the sentiments of vice and virtue are natural in this sense, we make no very extraordinary discovery.