Sextus Empiricus Pyrrhoniae Hypotyposes 2.4.21

[21] We suppose, then, that this is sufficient to expose the rashness of the Dogmatists in respect of their doctrine of the Criterion; but in order to enable us to confute them in detail, it will not be out of place to dwell at length upon this topic. We do not, however, desire to oppose their opinions about the criterion severally, one by one—for their controversy is endless, and to do so would necessarily involve us as well in a confused discussion,—but inasmuch as the criterion in question is three-fold (the agent, the instrument, and the ‟according to what”), we shall discuss each of these in turn and establish the non- apprehensibility of each, since in this way our exposition will be at once both methodical and complete. Let us begin with the agent; for the perplexity which attaches to this seems somehow to involve the rest as well.