This distinction is very important, as can be seen from any practical parallel. Suppose we wake up in the middle of the night and find that a neighbour has entered the house not by the front-door but by the skylight; we may suspect that he has come after the fine old family jewellery. We may be reassured if he can refer it to a really exceptional event; as that he fell on to the roof out of an aeroplane, or climbed on to the roof to escape from a mad dog. Short of the incredible, the stranger the story the better the excuse; for an extraordinary event requires an extraordinary excuse. But we shall hardly be reassured if he merely gazes at us in a dreamy and wistful fashion and says, "After all, what is property? Why should material objects be thus artificially attached, etc., etc.?" We shall merely realise that his attitude allows of his taking the jewellery and everything else. Or if the neighbour approaches us carrying a large knife dripping with blood, we may be convinced by his story that he killed another neighbour in self-defence, that the quiet gentleman next door was really a homicidal maniac. We shall know that homicidal mania is exceptional and that we ourselves are so happy as not to suffer from it; and being free from the disease may be free from the danger. But it will not soothe us for the man with the gory knife to say softly and pensively "After all, what is human life? Why should we cling to it? Brief at the best, sad at the brightest, it is itself but a disease from which, etc., etc." We shall perceive that the sceptic is in a mood not only to murder us but to massacre everybody in the street. Exactly the same effect which would be produced by the questions of "What is property?" and "What is life?" is produced by the question of "What is liberty?" It leaves the questioner free to disregard any liberty, or in other words to take any liberties. The very thing he says is an anticipatory excuse for anything he may choose to do. If he gags a man to prevent him from indulging in profane swearing, or locks him in the coal cellar to guard against his going on the spree, he can still be satisfied with saying, "After all, what is liberty? Man is a member of, etc., etc." That is the problem, and that is why there is now no protection against Eugenic or any other experiments. If the men who took away beer as an unlawful pleasure had paused for a moment to define the lawful pleasures, there might be a different situation. If the men who had denied one liberty had taken the opportunity to affirm other liberties, there might be some defence for them. But it never occurs to them to admit any liberties at all. It never so much as crosses their minds. Hence the excuse for the last oppression will always serve as well for the next oppression; and to that tyranny there can be no end.