Sextus Empiricus Pyrrhoniae Hypotyposes 1.14.60

[60] Besides, we are unable, either with or without proof, to prefer our own impressions to those of the irrational animals. For in addition to the probability that proof is, as we shall show, ¹ a non-entity, the so-called proof itself will be either apparent to us or non-apparent. If, then, it is non-apparent, we shall not accept it with confidence; while if it is apparent to us, inasmuch as what is apparent to animals is the point in question and the proof is apparent to us who are animals, it follows that we shall have to question the proof itself as to whether it is as true as it is apparent.