Sextus Empiricus Pyrrhoniae Hypotyposes 3.28.253

[253] Thus, for instance, the matter of instruction is either true or false; if false it would not be taught; for they assert that falsehood is non-existent, and of non-existents there could be no teaching. Nor yet if it were said to be true; for we have shown in our chapter ‟On the Criterion” ¹ that truth is non-existent. If, then, neither the false nor the true is being taught, and besides these there is nothing capable of being taught (for no one, to be sure, will say that, though these are unteachable, he teaches only dubious lessons ² ), then nothing is taught.