The Stoic Philosophy
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interest was in the first, but it could not be answered without first facing the second. For if we do not in the least know what is true or untrue, real or unreal, we cannot form any reliable rules, about conduct or anything else. And, as it happened, the Sceptical school of philosophy, largely helped by Plato, had lately been active in denying the possibility of human knowledge and throwing doubt on the very existence of reality. Their arguments were extraordinarily good, and many of them have not been answered yet; they affect both the credibility of the senses and the supposed laws of reasoning. The Sceptics showed how the senses are notoriously fallible and contradictory, and how the laws of reasoning lead by equally correct pro-
