“When in the Republic Thrasymachus says that justice is in the interest of the stronger, and Socrates starts to question him about this, Thrasymachus should hit Socrates over the head,” writes Robert Nozick in Philosophical Explanations.

He concedes too much when he enters an activity, discussion, that assumes that there is some mark of correctness and rightness other than (and superior to) strength. Similarly, there are norms of discussion that Thrasymachus draws upon — for instance, that anyone’s objection put seriously and sincerely ought to be replied to — and these norms, too, are incompatible with the position he states. Must the stronger also reply to an objection, if it is not in his interest?

Nozick returns to Thrasymachus’ surrender in his discussion of moral dialogue:

When someone raises a moral objection to something we are doing or planning, we feel we owe him an answer, a moral answer. It will not do simply to hit him on the head or to shrug our shoulders. An ethical egoist would reply only if he thought doing so was in his own interest; we feel we have to respond with moral reasons. (However, we do not have to expend our life’s savings to track down the person who objected and then went off to travel in inaccessible places. We ought to respond, prima facie, although this ‘ought’ can be overridden by other considerations.) Only by responding are we treating him as a value-seeking I; the only way to respond to his requesting moral reasons or raising moral objections, the only response to it qua that, is to offer moral reasons in justification or defense of our actions, to engage, if need be, in a moral dialogue with him. (Recall our earlier remark about how Thrasymachus undercuts his own position by engaging in discussion.) To engage in moral dialogue with someone is itself a moral act, whose moral character does not lie solely in being an attempt to get at the moral truth, or in being a vehicle to change and deepen a personal relationship and thereby be a means toward resolving moral conflict. Rather, (sincere) engagement in moral dialogue is itself a moral response to the other’s basic moral characteristic [as a value-seeking I], apart from its being a means toward satisfactory accommodation with the other. It is itself responsive to him; perhaps that is why openness in moral dialogue, considering carefully and responding closely to the concerns of the other, so often is an effective means toward resolution of conflict. When each is aware that the other is responsive to his or her own (valuable) characteristics in the very act of discussion and in the course the discussion takes, then this noticing of mutual respect is itself a force for good will and the moderation of demands; the altered conditions created by the dialogue may fit different moral principles so that new solutions are appropriate.

A moral dialogue of this sort is an especially clear example of a mutual value-theoretic situation…where each participant is responsive to the other’s basic moral characteristic, is aware that the other is responsive to her own, and is responsive to the other’s responsiveness, is aware of the other’s second-level responsiveness and is responsive to it, and so on….We want to be in mutual value-theoretic situations; only then is the value in us (including our own value responsiveness) adequately answered. Hegel’s discussion of the master-slave relation elaborates how domination thwarts this; the master cannot force this responsiveness from the slave, and unless the master shows responsiveness to the slave’s basic moral characteristic (but then he could not remain his master) the slave cannot respond to that.