I am not making idle play with the word "destruction." It is literally true that in human society the most destructive and the most coercive forces at work are ideas. They strike at established institutions and demand either their modification or their removal. That is why the emergence of a new idea is always an event of social significance. Whether it be a good idea or a bad one will not affect the truth of this statement. For over four years our political mediocrities and muddle headed militarists were acting as though the real problem before them was to establish the superiority of one armed group of men over another group. That was really a simple matter. The important issue which society had to face was the ideas that the shock of the war must give rise to. Thinkers saw this; but thinkers do not get the public ear either as politicians or militarists. And now events are driving home the lesson. The ideas of Bolshevism and Sinn Feinism proved far more "dangerous" than the German armies. The Allied forces could handle the one, but they were powerless before the other. It is not a question of whether these particular ideas are good or bad, or whether we approve or disapprove of them, but entirely one that, being ideas, they represent a far more "destructive" power than either bomb or gun. They are at once the forces that act as the cement of society and those that may hurl it into chaotic fragments. Whether an idea will survive or not must, in the end, be determined by circumstances, but in itself a new idea may be taken as the mental analogue of the variation which takes place in physical structures, and which forms the raw material of natural selection. And if that is so, it is evident that any attempt to prevent the play of new ideas on old institutions is striking at the very fact of progress. For if we are to encourage variation we must permit it in all directions, up as well as down, for evil as well as for good. You cannot check variation in one direction without checking it in all. You cannot prevent the appearance of a new idea that you do not want without threatening the appearance of a number of ideas that you would eagerly welcome. It is, therefore, always better to encourage the appearance of a bad idea than it is to risk the suppression of a good one. Besides, it is not always that force applied to the suppression of ideas succeeds in its object. What it often does is to cause the persecuted idea to assume a more violent form, to ensure a more abrupt break with the past than would otherwise occur, with the risk of a period of reaction before orderly progress is resumed. The only way to silence an idea is to answer it. You cannot reply to a belief with bullets, or bayonet a theory into silence. History contains many lessons, but none that is plainer than this one, and none that religious and secular tyrannies learn with greater reluctance.