Sextus Empiricus Pyrrhoniae Hypotyposes 2.1.4

[4] Now let those who speak thus make answer and tell us in what sense they are now using the term ‟apprehend,” whether simply of mental conception without the further affirmation of the reality of the objects under discussion, or with the further assumption of the reality of the objects discussed. For if they say that ‟to apprehend” means, in their argument, to assent to an ‟apprehensive impression,” ¹ the apprehensive impression being derived from a real object and being an imprint or stamp upon the mind corresponding to the actual object, such as would not result from what is unreal, then probably not even they themselves will wish to allow their inability to investigate things which, in this sense, they have not apprehended.