Justice is the set and constant purpose which gives to every man his due. Wild animals, birds, and fish, that is to say all the creatures which the land, the sea, and the sky produce, as soon as they are caught by any one become at once the property of their captor by the law of nations. The study of law consists of two branches: law public and law private. The laws of every people governed by statutes and customs are partly peculiar to itself, partly common to all mankind. Private law is of threefold origin: being collected from the precepts of nature, from those of the law of nations, or from those of the civil law of Rome. The law of nations is common to the whole human race; for nations have settled certain things for themselves as occasion and the necessities of human life required.