Knowing so little of nature, and agreeing so ill about the meaning of the word _law_, it would be difficult for us to fix on a good definition of natural law. Thus all the definitions we meet with in books, setting: aside their defect in point of uniformity, have yet another fault, in that they are derived from many kinds of knowledge, which men do not possess naturally, and from advantages of which they can have no idea until they have already departed from that state. Modern writers begin by inquiring what rules it would be expedient for men to agree on for their common interest, and then give the name of natural law to a collection of these rules, without any other proof than the good that would result from their being universally practised. This is undoubtedly a simple way of making definitions, and of explaining the nature of things by almost arbitrary conveniences. But as long as we are ignorant of the natural man, it is in vain for us to attempt to determine either the law originally prescribed to him, or that which is best adapted to his constitution. All we can know with any certainty respecting this law is that, if it is to be a law, not only the wills of those it obliges must be sensible of their submission to it; but also, to be natural, it must come directly from the voice of nature. Throwing aside, therefore, all those scientific books, which teach us only to see men such as they have made themselves, and contemplating the first and most simple operations of the human soul, I think I can perceive in it two principles prior to reason, one of them deeply interesting us in our own welfare and preservation, and the other exciting a natural repugnance at seeing any other sensible being, and particularly any of our own species, suffer pain or death. It is from the agreement and combination which the understanding is in a position to establish between these two principles, without its being necessary to introduce that of sociability, that all the rules of natural right appear to me to be derived--rules which our reason is afterwards obliged to establish on other foundations, when by its successive developments it has been led to suppress nature itself.