“I never was satisfied with the description given of the law of nations, commonly so called, That it is a law established among nations by common consent, for regulating their conduct with regard to each other. This foundation of the law of nations I take to be chimerical. For upon what occasion was this covenant made, and by whom? If it be said, that the sense of common good gradually brought this law into force; I answer, that the sense of common good is too complex and too remote an object to be a solid foundation for any positive law, if it have no other foundation.
“But there is no necessity to recur to so slender a foundation. What is just now observed, will lead us to a more rational account of these laws. They are no other but gradual refinements of the original law of nature, accommodating itself to the improved state of mankind. The law of nature, which is the law of our nature, cannot be stationary: it must vary with the nature of man, and consequently refine gradually as human nature refines. Putting an enemy to death in cold blood, raises at present distaste and horror, and therefore is immoral; though it was not always so in the same degree. It is considered as barbarous and inhuman to fight with poisoned weapons; and therefore is more remarkably disapproved by the moral sense than it was originally.
“Influenced by general objects, we have enmity against France, our natural enemy. But this enmity is not directed against individuals; conscious, as we are, that it is the duty of subjects to serve their king and country. Therefore we treat the prisoners of war with humanity. And now it is creeping in among civilized nations, that in war a cartel should be established for exchange of prisoners. The function of an ambassador has ever been held sacred. To treat him ill was originally immoral; because it is treating as an enemy the man who comes to us with friendly intentions. But the improved manners of later times have refined upon the privileges of an ambassador, and extended them far beyond what they were originally. It is true, that these refinements of the law of nature gain strength and firmness from constant exercise. Hereby they acquire the additional support of common consent. And as every nation trusts that these laws will be observed, it is upon that account a breach of faith to transgress them. But this is not peculiar to these institutions which pass under the name of the law of nations. There is the same adventitious foundation for all the laws of nature, which every man trusts will be observed, and upon that faith directs his conduct.”
- Henry Home Kames, from Essays on the Principles of Morality and Natural Religion