Sextus Empiricus Pyrrhoniae Hypotyposes 2.13.175

[175] Moreover, since they assert that proof is a relative thing and relative to the inference, and relatives, as they themselves affirm, are conceived in relation to other things, the thing proved must be other than the proof ; if, then, the thing proved is the conclusion, the proof will not be conceived along with the conclusion. For the conclusion either contributes something to its own proof or does not do so; but if it contributes, it will serve to reveal itself, while if it does not contribute but is redundant it will not be even a part of the proof, since we shall declare the proof to be faulty by reason of redundance.