The traits which give thinking effectiveness for the good give it also potency for harm. A physical catastrophe, an earthquake or conflagration, acts only where it happens. While its effects endure, it passes away. But it is of the nature of ideas to be abstract: that is to say, severed from the circumstances of their origin, and through embodiment in language capable of operating in remote climes and alien situations. Time heals physical ravages, but it may only accentuate the evils of an intellectual catastrophe--for by no lesser name can we call a systematic intellectual error. To one who is professionally preoccupied with philosophy there is much in its history which is profoundly depressing. He sees ideas which were not only natural but useful in their native time and place, figuring in foreign contexts so as to formulate defects as virtues and to give rational sanction to brute facts, and to oppose alleged eternal truths to progress. He sees movements which might have passed away with change of circumstance as casually as they arose, acquire persistence and dignity because thought has taken cognizance of them and given them intellectual names. The witness of history is that to think in general and abstract terms is dangerous; it elevates ideas beyond the situations in which they were born and charges them with we know not what menace for the future. And in the past the danger has been the greater because philosophers have so largely purported to be concerned not with contemporary problems of living, but with essential Truth and Reality viewed under the form of eternity. In bringing these general considerations to a close, I face an embarrassment. I must choose some particular period of intellectual history for more concrete illustration of the mutual relationship of philosophy and practical social affairs--which latter, for the sake of brevity, I term Politics. One is tempted to choose Plato. For in spite of the mystic and transcendental coloring of his thought, it was he who defined philosophy as the science of the State, or the most complete and organized whole known to man; it is no accident that his chief work is termed the "Republic." In modern times, we are struck by the fact that English philosophy from Bacon to John Stuart Mill has been cultivated by men of affairs rather than by professors, and with a direct outlook upon social interests. In France, the great period of philosophy, the period of _les philosophes_, was the time in which were forged the ideas which connect in particular with the French Revolution and in general with the conceptions which spread so rapidly through the civilized world, of the indefinite perfectibility of humanity, the rights of man, and the promotion of a society as wide as humanity, based upon allegiance to reason.