Natural Law

At the heart of natural law is an attempt to extract general principles out of the confusing multiplicity of legal and social convention; in the Greek world, this was represented by the contrast and tension between those areas of human life governed by contingency and those controlled by the ineluctable force of nature. Given the variability of positive law both across cultures and within them, the question arose of how legal certainty could be identified and located; and immediately battle-lines were drawn between those who held that such a moral law could be found—usually as a divine creation—and those who remained skeptical of such normative claims, and either denied that there was any essential morality, or located it elsewhere. This pattern, which originated with the Sophists, was to be repeated throughout the history of natural law arguments.

Part of the explanation of why Aristotle's writings are regarded as the first important contribution to this discourse is that they adeptly try to reconcile the distinction between nature and convention. He achieves this by elevating human reason as humankind's dominant and defining characteristic, whose proper exercise mediates between what is permanent and what is ephemeral. This is taken up with greater vigor by the Stoics, and by Marcus Tullius Cicero (106–43 B.C.E.) in particular. He regarded human reason as the apex of a rational world order: human nature rather than an innate law outside human beings now provided the ground and basis for distinguishing between positive law and natural law. Moreover, all humans possessed the rational means, when properly exercised, to identify this law unaided by God, whose divine spark reason essentially is. The Stoics also initiated what was to become one of the most influential strands of natural law thinking—namely, the view that one of the core principles of natural law is a sense of broad sociability towards one's fellow humans, tempered though not obliterated by one's own personal priorities.

The rationalism of natural law still runs as a clear thread through the massive Summa Theologiae of Aquinas, despite its elaborate metaphysical architecture. Human nature and the rational conclusions that can be generated from it continue to be his point of departure. However, Aquinas is concerned to reinstate divine eternal law within his framework, and that does lead to some tension within his overall concept of natural law as a bridge between positive and divine law. He tries to overcome this by recourse to a categorical division of natural law into primary and secondary principles, thus making natural law both fixed and mutable simultaneously. This sophisticated synthesis of pre-existing views within a Christian framework proved highly influential, and was continually refined, most notably by the later Spanish Jesuit Francisco Suarez (1548–1617); but ultimately the pressures generated by the Reformation and Thirty Years' War on the one hand and Renaissance skepticism on the other required a reconfiguring of the relationship between divine and natural law, a renewed emphasis on the Stoic formulas, and a fresh initiative to link the core principles of natural law to the emergent law of nations.