Thrasymachus, Reasons and Rationality
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Thrasymachus, in Plato’s Republic, claims that justice is what is in the interest of the stronger party. Cross and Woozley interpret this as the claim that the weak have a duty to serve the interests of the strong. I argue that this interpretation is mistaken and that Thrasymachus agrees with Socrates (and Aristotle) that justice is giving people their fair share. Thrasymachus’ point is that people who act justly in effect are serving the interests of the stronger and, thereby, are acting irrationally. For Thrasymachus, the rational thing to do is to pursue your own self-interest even if it is at the expense of others. Thrasymachus seems to be adopting an instrumentalist account of rationality here. I contrast this with the kind of objectivist account of rationality offered by philosophers like Scanlon, Parfit and Nagel which maintains that there are substantive reasons why one should sometimes pursue the interests of others for its own sake. I argue that this apparent objectivity is an artifact of how talk about reasons works in public, as opposed to private, reasoning. I conclude that Thrasymachus is correct that egoism is rational, but he is mistaken to think that it is the only rational position. Acting justly is also rational. I conclude that, while a just person is rational in sincerely advocating justice, Thrasymachus is irrational in sincerely advocating egoism.
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