The problems of authority, law and order, obligation, and self-interest first became central topics of speculation in the thought of the Sophists (late fifth and early fourth centuries BCE). The most famous Sophists all stressed the distinction between nature (physis) and convention (nomos), and they put laws in the latter category. They generally attributed law to human invention and justified obedience to law only to the extent that it promoted one's own advantage. Laws were artificial, arrived at by consent; the majority of acts that were just according to the law were contrary to nature; the advantages laid down by the law were chains upon nature, but those laid down by nature were free. In the time of the Sophists notions of law, justice, religion, custom, and morality were largely undifferentiated; yet in this same period some of the crucial...