Sextus Empiricus Pyrrhoniae Hypotyposes 2.5.42

[42] And even should we grant, by way of concession, that no one either is, was, or will be more sagacious than our hypothetical Sage, not even so is it proper to believe him. For since it is the sagacious above all who, in the construction of their doctrines, love to champion unsound doctrines and to make them appear sound and true, whenever this sharp-witted person makes a statement we shall not know whether he is stating the matter as it really is, or whether he is defending as true what is really false and persuading us to think of it as something true, on the ground that he is more sagacious than all other men and therefore incapable of being refuted by us. So not even to this man will we assent, as one who judges matters truly, since, though we suppose it possible that he speaks the truth, we also suppose that owing to his excessive cleverness he makes his statements with the object of defending false propositions as true. Consequently, in the judgement of propositions we ought not to believe even the man who is thought to be the most clever of all.