In discussing the organization of society, Cicero finds the source of law and justice, not in utility, but in nature. Right and wrong are determined _naturae norma_, (_De Legibus_, I. 16. 44). This law of nature is not one thing in Rome, another in Athens; it is not one thing today, another tomorrow, but it is eternal and immutable, (_De Re Publica_, III. 22. 33). This conception of the _ius naturale_ was taken up by Ulpian in the third century and by other early jurists, developed in the _Code_ of Justinian, and handed down through the Middle Ages to our own time. It covers “that body of principles of justice and reason which men can rationally apprehend, and which forms the ideal norm or standard of right conduct and of the justice of social institutions.” From the Civil law it passed into Canon law through the encyclopedic work of St. Isidore in the seventh century, and gave rise to the tripartite division which Gratian sets forth in the _Decretals_, when he writes: “_Ius naturale_ appears with the beginnings of the rational creation, and remains unchangeable: the _ius consuetudinis_ (i.e., the _ius gentium_) had its inception later, when men began to live together.... But the _ius constitutionis_ (i.e., the _ius civile_) begins with the principles which the Lord delivered to Moses,” i.e., with written law. These distinctions have furnished the starting point in most modern discussions of the subject. Cicero defined the Commonwealth as “the affair of the people, but the people is not any assemblage of men, gathered together in any fashion, but a gathering united under a common law and in the enjoyment of a common well being,” (_De Re Publica_, I. 25. 39). From this definition he seems to imply that the state has a twofold purpose, to protect the individual, and to promote his welfare. In one passage in his _Commonwealth_, (_De Re Publica_, III. 13. 23), he makes a speaker in the dialogue enunciate a theory of the state, out of which Rousseau may well have developed his doctrine of the Social Contract: “But when one person fears another, when man fears man, and class, class, then, since no one trusts his own strength, a compact is made between the people and the rulers, out of which springs that which Scipio approved--a state whose form is determined by agreement.” This theory of the Social Compact, probably derived from Cicero, was put forth again in the eleventh century. So far as the form of the state goes, it may be monarchical, aristocratic, or democratic, or these three elements may be combined in it, as Cicero thought they were in the Roman state; Cicero followed Aristotle and particularly Polybius, in the latter’s discussion of the constitutions of Rome and Sparta. The views which Cicero held on this point were taken up for consideration and emphatically denied by Jean Bodin in his great work on the state in the sixteenth century.