Fronton du Duc notes that Basil has taken this allusion to Plato from Plutarch’s tract, How to distinguish between Flatterer and Friend, p. 50:  ὡςγὰρ ὁ Πλάτων φησὶν ἐσχάτης ἀδικίας εἶναι δοκεῖν δίκαιον μὴ ὄντα.