By far the most detailed surviving examination by any ancient Greek sceptic of epistemology and logic, this work critically reviews the pretensions of non-sceptical philosophers, to have discovered methods for determining the truth, either through direct observation or by inference from the observed to the unobserved. A fine example of the Pyrrhonist sceptical method at work, it also provides extensive information about the ideas of other Greek thinkers, which in many instances, are poorly preserved in other sources.