The turning of the tables, whereby Plato (Theaetetus, 171a) opposes the relativism of Protagoras. Protagoras allegedly holds the doctrine that whatever seems true for a person is true for them. Hence he must accept that those who believe that this doctrine of Protagoras is false are right: its falsity is true for them. It became a standard form of argument against relativism, used by both Epicurus and Sextus Empiricus and down to present times. See also Ishmael effect.