Great changes are not caused by ideas alone; but they are not effected without ideas. The passions of men must be aroused if the frost of custom is to be broken or the chains of authority burst; but passion of itself is blind and its world is chaotic. To be effective men must act together, and to act together they must have a common understanding and a common object. When it comes to be a question of any far-reaching change, they must not merely conceive their own immediate end with clearness. They must convert others, they must communicate sympathy and win over the unconvinced. Upon the whole, they must show that their object is possible, that it is compatible with existing institutions, or at any rate with some workable form of social life. They are, in fact, driven on by the requirements of their position to the elaboration of ideas, and in the end to some sort of social philosophy; and the philosophies that have driving force behind them are those which arise after this fashion out of the practical demands of human feeling. The philosophies that remain ineffectual and academic are those that are formed by abstract reflection without relation to the thirsty souls of human kind. In England, it is true, where men are apt to be shy and unhandy in the region of theory, the Liberal movement has often sought to dispense with general principles. In its early days and in its more moderate forms, it sought its ends under the guise of constitutionalism. As against the claims of the Stuart monarchy, there was a historic case as well as a philosophic argument, and the earlier leaders of the Parliament relied more on precedent than on principle. This method was embodied in the Whig tradition, and runs on to our own time, as one of the elements that go to make up the working constitution of the Liberal mind. It is, so to say, the Conservative element in Liberalism, valuable in resistance to encroachments, valuable in securing continuity of development, for purposes of re-construction insufficient. To maintain the old order under changed circumstances may be, in fact, to initiate a revolution. It was so in the seventeenth century. Pym and his followers could find justification for their contentions in our constitutional history, but to do so they had to go behind both the Stuarts and the Tudors; and to apply the principles of the fourteenth and fifteenth centuries in 1640 was, in effect, to institute a revolution. In our own time, to maintain the right of the Commons against the Lords is, on the face of it, to adhere to old constitutional right, but to do so under the new circumstances which have made the Commons representative of the nation as a whole is, in reality, to establish democracy for the first time on a firm footing, and this, again, is to accomplish a revolution.