But nature may also be opposed to rare and unusual; and in this sense of the word, which is the common one, there may often arise disputes concerning what is natural or unnatural; and one may in general affirm, that we are not possessed of any very precise standard, by which these disputes can be decided.  Frequent and rare depend upon the number of examples we have observed; and as this number may gradually encrease or diminish, it will be impossible to fix any exact boundaries betwixt them.  We may only affirm on this head, that if ever there was any thing, which coued be called natural in this sense, the sentiments of morality certainly may; since there never was any nation of the world, nor any single person in any nation, who was utterly deprived of them, and who never, in any instance, shewed the least approbation or dislike of manners.  These sentiments are so rooted in our constitution and temper, that without entirely confounding the human mind by disease or madness, it is impossible to extirpate and destroy them.

But nature may also be opposed to artifice, as well as to what is rare and unusual; and in this sense it may be disputed, whether the notions of virtue be natural or not.  We readily forget, that the designs, and projects, and views of men are principles as necessary in their operation as heat and cold, moist and dry:  But taking them to be free and entirely our own, it is usual for us to set them in opposition to the other principles of nature. should it, therefore, be demanded, whether the sense of virtue be natural or artificial, I am of opinion, that it is impossible for me at present to give any precise answer to this question.  Perhaps it will appear afterwards, that our sense of some virtues is artificial, and that of others natural.  The discussion of this question will be more proper, when we enter upon an exact detail of each particular vice and virtue.

[Footnote 14.  In the following discourse natural is also opposed sometimes to civil, sometimes to moral.  The opposition will always discover the sense, in which it is taken.]

Mean while it may not be amiss to observe from these definitions of natural and unnatural, that nothing can be more unphilosophical than those systems, which assert, that virtue is the same with what is natural, and vice with what is unnatural.  For in the first sense of the word, Nature, as opposed to miracles, both vice and virtue are equally natural; and in the second sense, as opposed to what is unusual, perhaps virtue will be found to be the most unnatural.  At least it must be owned, that heroic virtue, being as unusual, is as little natural as the most brutal barbarity.  As to the third sense of the word, it is certain, that both vice and virtue are equally artificial, and out of nature.  For however it may be disputed, whether the notion of a merit or demerit in certain actions be natural or artificial, it is evident, that the actions themselves are artificial, and are performed with a certain design and intention; otherwise they coued never be ranked under any of these denominations.  It is impossible, therefore, that the character of natural and unnatural can ever, in any sense, mark the boundaries of vice and virtue.