Pyrrho of Elis, a rather earlier teacher than Zeno or Epicurus, who is said to have studied philosophy under Indian Gymnosophists and Chaldean Magi, was the originator in European thought of a great and permanent philosophic movement. His school was inspired by the _Geist der stets verneint_, and the term Skeptic was first devised to describe its attitude. Its strength is in a discovery which inevitably takes place when men begin to reflect upon their own mental operations—the discovery, namely, that, given a perceiving mind and a perceived object, it is always possible for the former, if it has the power of introspection, to doubt whether it has received a really true and faithful impression of the latter. How can we be assured that external objects are as we perceive them? How can we even be assured that there is any principle of constancy in their relations to our consciousness? The senses often delude us; we are convinced, in dreams, of the reality of appearances which, nevertheless, have no reality—why may not all perception be a delusion? Why may not even our sense of the validity of inference and of the truth of the axioms of geometry be a pure hallucination? With these searching questions the Skeptic cut at the root of all belief, and the problems which they raise have dominated philosophy down to the present day. Nor in two thousand years has any logical answer to them ever been found. Lotze, the last thinker of really first-rate powers that the world has seen, practically abandons all inquiry into theories of perception, and starts with the _assumption_ that we are living in a kosmos, not a chaos; that the order, coherence, reason in things to which consciousness testifies, are realities. In antiquity, I may add, the profound problems raised by Pyrrhonism do not seem to have been very profoundly apprehended either by the Pyrrhonists or their opponents. The latter had nothing better to appeal to than that notoriously feeble resource, the _argumentum ad hominem_. If the Pyrrhonist distrusted the evidence of his senses, they asked, why did he avoid walking over precipices or into the sea, or eat bread instead of earth, or in any way make choice of means for ends? The Pyrrhonist’s answer was equally superficial. It anticipated the famous formula of Bishop Butler. Probability, argued they, was the guide of life—having observed certain results to follow from certain antecedents, the prudent man will shape his course in life accordingly, although, as a matter of theory and speculation, he may refuse to believe in the constancy of nature. This answer involves a clear inconsistency. It involves even a greater assumption than that which the Pyrrhonist refused to make as to the credibility of his perceptions—the assumption of the credibility of his recollections. To the thorough-going Skeptic there is no such thing as past experience—he is, as it were, new-born at each instant of his life.