The recognition of these simple modes of contracting obligations, and perhaps the knowledge that certain rules of law obtained among many peoples, fostered the conception of common or natural justice, which human reason was supposed to inculcate everywhere. Such a conception could not fail to spring up in the minds of Roman jurists who were educated in Stoical philosophy, the ethics of which had much to say of a common human nature. Indeed the idea naturalis ratio was in the air, and the thought of common elements of law and justice which naturalis ratio inter omnes homines constituit, lay so close at hand that it were perhaps a mistake to try to trace it to any single source. Practically the jus gentium became identical with jus naturale, which Ulpian imagined as taught by nature to all animals; the jus gentium, however, belonged to men alone.[1]
Thus rules which were conceived as those of the jus gentium came to represent the principles of rational law, and impressed themselves upon the development of the jus civile. They informed the whole growth and application of Roman law with a breadth of legal reason. And conceptions of a jus naturale and a jus gentium became cognate legal fictions, by the aid of which praetor and jurisconsult might justify the validity of informal modes of contract. In their application, judge and jurist learned how and when to disregard the formal requirements of the older and stricter Roman law, and found a way to the recognition of what was just and convenient. These fictions agreed with the supposed nature and demands of aequitas, which is the principle of progressive and discriminating legal justice. Law itself (jus) was iden-
- ↑ Dig. i. 1 ("De Just, et jure") 1. See Savigny, System deshcutigen romischen Rechts, i. p. 109 sqq. Apparently some of the jurists (e.g. Gaius, Ins. i. 1) draw no substantial distinctions between jus naturale and the jus gentium. Others seem to distinguish. With the latter, jus naturale might represent natural or instinctive principles of justice common to all men, and jus gentium, the laws and customs which experience had led men to adopt. For instance, libertas is jure naturali, while dominatio or servitus is introduced ex gentium jure (Dig. i. 5, 4; Dig. xii. 6, 64). Jus gentium represented common expediency, but its institutions (e.g. servitus) might or might not accord with natural justice. For manumissio as well as servitus was ex jure gentium (Dig. i. 1, 4), and so were common modes and principles of contract. Ulpian's notion of the jus naturale as pertaining to all animals, and jus gentium as belonging to men alone, was but a catching classification, and did not represent any commonly followed distinction.
