Sextus Empiricus Pyrrhoniae Hypotyposes 2.13.187

[187] Now to this we may reply, for instance, that, because we do not believe that any argument is probative, we do not assert either that the arguments against proof are absolutely probative but that they appear to us plausible; but those that are plausible are not necessarily probative. Yet if they actually are probative (which we do not positively affirm) they certainly are also true. And true arguments are those which deduce what is true by means of true premisses; wherefore their inference is true. Now the inference was this—‟therefore proof does not exist;” therefore the statement ‟proof does not exist” is true by reversing the argument.