  Protagoras’ account of social morality in the Great Speech, according to which the universal acceptance of justice and self-restraint is necessary for the perpetuation of society, and thereby for the preservation of the human species, places Protagoras firmly on one side (the conservative side, we should note) of the debate about the relation between law and convention (nomos) on the one hand and nature or reality (phusis) on the other, which was central to moral and social thought in the fifth and fourth centuries. The debate was fundamentally about the status of moral and other social norms; were such norms ever in some sense part of or grounded in the reality of things, or were they in every case mere products of human customs, conventions or beliefs? The question was crucial to the perceived authority of norms; both sides agreed in seeing nature as authoritative for correct human behavior, and as the ultimate source of true value. Critics of traditional morality argued that since that morality was nothing more than a human invention it thereby lacked genuine authority (which belonged to the realm of nature), thus sanctioning violation of traditional moral norms if the violator could escape punishment or other bad consequences (while ‘following nature’), while the upholders of morality sought to show that morality, as reflected in traditional norms, was itself in some sense a part or product of nature. We find examples of the critical stance both in some Platonic dialogues and in some sophistic writings. The starkest expression of the opposition between nomos and phusis is that expressed in the Gorgias by Callicles, a pupil of Gorgias (though there is no suggestion in the dialogue or elsewhere that Gorgias himself held that position): Callicles holds that conventional morality is a contrivance devised by the weak and unintelligent to inhibit the strong and intelligent from doing what they are entitled by nature to do, viz. exploit their inferiors for their own advantage. He is thus an inverted moralist, who holds that what it is really right to do is what it is conventionally wrong to do. The true, authoritative norms are those which prevail in nature, as shown by the behavior of non-human animals such as beasts of prey; those who act in accordance with these norms ‘do these things in accordance with the nature of justice and … the law of nature, but perhaps not in accordance with this one which we lay down’ (Plato, Gorgias, 483e). The sophist Thrasymachus maintains a similar position in Book I of the Republic, though without Callicles’ daring inversion of values. He agrees with Callicles in praising the ruthless individual (above all the tyrant) who is capable of overcoming the restraints of morality, but whereas Callicles calls such self-assertion naturally just, Thrasymachus abides by conventional morality in calling it unjust. Both agree that a successful life of ruthless self-assertion is supreme happiness, and that that is what nature prompts us to seek; both, then, accept the normative authority of nature over nomos. The difference between them is that Callicles takes the further step of identifying the authority of nature with that of real, as opposed to conventional morality, whereas for Thrasymachus there is only one kind of morality, conventional morality, which has no authority. In Book II Glaucon presents a modified version of Thrasymachus’ position; while maintaining, as Protagoras does in the Great Speech, that humans adopt moral conventions as a necessary survival strategy in a hostile world, he insists that this involves a stunting of human nature, since people are obliged for self-protection to abandon the goal of self-satisfaction to which nature, as Thrasymachus insists, prompts them. This assertion of egoism is supported by the thought-experiment of Gyges’ ring; if, like the legendary Gyges, we had a magic ring which rendered us invisible, and hence immune from sanctions, we would all seek our own interest without restraint. We find a similar down-grading of convention in favor of nature (though one lacking the immoralist conclusions) in Hippias’ speech in the Protagoras (337c–d), where he urges that intellectuals such as are gathered in the house of Callias ought not to quarrel, since, though according to artificial political conventions they are citizens of many different cities, by nature they are all akin. The conventions which make them treat each other as strangers distort the reality by which they are all alike; hence they should recognise that reality by treating each other as friends and members of the same family, not as strangers. (The vignette gains added point from the fact that Hippias, speaking in Athens, is a citizen of Elis, a Peloponnesian state allied to Sparta in the war against Athens.) Outside Plato the most extended and explicit expression of the ‘antinomian’ stance is a well-known papyrus fragment of Antiphon (DK 87B44), which presents a number of contrasts between the requirements of conventional morality and those of nature, to the disadvantage of the former. Nature prompts us to do only what is advantageous to us, and if we try to act contrary to its promptings we inevitably suffer for it as a natural consequence, whereas morality typically restrains us from doing what is advantageous to ourselves and requires us to do what is disadvantageous, and if we violate the requirements of morality we come to harm only if we are found out. Legal remedies are insufficient to prevent the law-abiding person from harm, since they are applicable only after the harm has been done, and there is always the chance that the law-abiding person will lose his case anyway. Another part of the papyrus (fragment B) suggests that some legal norms are self-contradictory; it is just to bear true witness in court, and unjust to wrong someone who has not wronged you. So someone who bears true witness against someone who has not wronged him (e.g., witness A who truly testifies that he saw B murder C) wrongs the person against whom he bears witness, and therefore acts both justly and unjustly. (The argument here depends on an illicit assimilation of harming with wronging: the witness certainly harms the murderer by his true testimony, assuming that it leads to his conviction and execution, but there is no reason to agree that in giving that testimony the witness wrongs the murderer.) Moreover, he thereby puts himself in danger of retaliation by the person whom he has wronged; so once again obedience to nomos is disadvantageous.