But that is a very small part of the business. The chief contribution of such justice to human liberty is that it supplies the necessary conditions of discipline without which there can be no liberty. We think of liberty as meaning freedom from external constraint. We think that an act of ours is free when we can say, "I did it, and no one made me do it"; but very little reflection is sufficient to convince us that a man whose life is actually governed by one or several over-developed passions which he will, as a matter of fact, always gratify when opportunity offers, in spite of the damage that is done to his whole life and to his permanent and deliberate purpose, is not really a free man. To be tied and bound with the chain of our sins is just as much slavery as to be in the ownership of another man; and we can acquire the real liberty which is worth having, the liberty, that is, to shape our lives, to live according to our own purpose, following out our own ideal, only in so far as our natures have been welded by discipline into unity, so that we are no longer a chaos of impulses and instincts, any of which may be set in motion by the appropriate environment, but are self-governing persons controlling our own lives. Liberty, in so far as it is of any value, always means self-control in both the senses of that term: in the sense that we are only controlled by ourselves, and also in the sense that by ourselves we are controlled, and that every part of our nature is subservient to the purpose to which our whole nature is given. Legislation is really an instrument of self-discipline. The people who write books about political philosophy are mainly members of the respectable classes. They naturally find it rather difficult to envisage themselves as liable to commit murder and the like; and they are therefore very liable to represent the criminal law of the State as being enacted against a few undisciplined or recalcitrant members. But when we look at the thing more closely, we see that what a community does, especially a democratic community, when it passes a law, is to invoke, every member upon his own head, the penalties enacted by that law, if he should do the act which the law forbids. Let us consider, for example, an international convention. What is the use of nations agreeing with one another not to do something, for instance not to poison wells, unless there is some chance that in a moment of strong temptation they may desire to do it? They therefore strengthen their deliberate purpose to avoid such acts by entering into an agreement with one another always to avoid them. There would be no object in doing this unless they needed help, or thought that they might at some time need help, in living up to their own purposes.