Sextus Empiricus Pyrrhoniae Hypotyposes 2.11.128

[128] And as to the non-evident signs which need things to reveal them, if we say that they are signified by things non-evident, the argument will be involved in a regress ad infinitum, rendering them non-apprehensible and therefore unreal, as we said before; ¹ whereas, if they are to be signified by things apparent, they will be apparent, because apprehended along with their apparent signs, and therefore also unreal. For it is impossible for any object really to exist which is by nature both non-evident and apparent; but the signs which we are discussing though assumed to be non-evident have been found to be apparent owing to the reversal of the argument. ²