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 increase or diminish, 'twill be impossible to fix any exact boundaries betwixt them. We may only affirm on this head, that if ever there was any thing which could 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, showed 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, 'tis 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, 'tis 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 'tis 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.[4]
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, 'tis 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, 'tis evident that the actions themselves are artificial, and are performed with a certain design and intention; otherwise they could never be ranked under any of these denominations. 'Tis impossible, therefore, that the character of natural and unnatural can ever, in any sense, mark the boundaries of vice and virtue.
Thus we are still brought back to our first position, that virtue is distinguished by the pleasure, and vice by the pain, that any action, sentiment, or character, gives us by the mere view and contemplation. This decision is very commodious; because it reduces us to, this simple question, Why any action or sentiment, upon the general view or survey, gives a certain satisfaction or uneasiness, in order to show the origin of its moral rectitude or depravity, without looking for any incomprehensible relations and qualities, which never did exist in nature, nor even in our imagination, by any clear and distinct conception? I flatter myself I have executed a great part of my present design by a state of the question, which appears to me so free from ambiguity and obscurity.
[4] 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.