Sextus Empiricus Pyrrhoniae Hypotyposes 1.17.186

[186] But if, on the other hand, the cause propounded be not in accord therewith, the theorist will be asked in turn for the cause of this cause, and if he assumes an apparent cause for an apparent, or a non-evident for a non- evident, he will be involved in the regress ad infinitum, or reduced to arguing in a circle if he grounds each cause in turn on another. And if at any point he makes a stand, either he will state that the cause is well-grounded so far as relates to the previous admissions, thus introducing relativity and destroying its claim to absolute reality, or he will make some assumption ex hypothesi and will be stopped by us. So by these Modes also it is, no doubt, possible to expose the rashness of the Dogmatists in their aetiologies.