Ever since the earliest times, grave men have meditated on the relation between Custom and Law. They were forced by evidence and practical experience to note a difference between the two institutions, but at the same time they had the definite impression that they trace their origin to the same source. Socrates distinguishes between the written laws of his country and the unwritten ones which express the will of the gods. The former constitute positive Law which the citizen must observe and to which he must submit; the latter, however, are higher, for they emanate from the gods themselves. The immutability of the unwritten laws is a proof that they are superior to the written ones. Written laws vary from state to state. They are the work of individual law-givers who were sometimes wise men and sometimes unreasonable tyrants. But all contain certain precepts which are everywhere alike, which everywhere impose the same rules upon man. It is almost as if one and the same law-giver had co-operated in the making of all the laws that obtain in the different towns and countries, and are so unlike one another in many points. This common law-giver, whose will is manifest in all laws, however far removed they be from one another, is the Deity. That is essentially Socrates' train of thought as given by Xenophon in his _Memorabilia_. The Attic sage speaks the language of his time, which, by the way, is still that of many present-day people. The Deity, whose will permeates all written laws and to whom they may be traced, is the principle of Morality. Hugo Grotius, in a manner more appropriate to modern thought, expresses it thus: "Law and Morality spring from the same source, namely, the strong social instinct natural to man. They bear witness to reasonable solicitude for the welfare of the community." This placing on an equality of Law and Custom, of _jus_ and _mos_, is very remarkable in such a strictly professional thinker, such a positive jurist as Grotius. Kant discriminates between the doctrine of Virtue and the doctrine of Law; he keeps them apart, but he emphasizes their connexion, and the two together make up his doctrine of Ethics.