Since that time a radical has come to mean any root-and-branch reformer; and radicalism itself may be defined as a tendency to abolish existing institutions or principles. As soon as either of these seems to have outlived its usefulness, radicalism will clamor for its suppression. Discontent, then, is a source of radicalism. This, however, is of a dual nature--discontent with conditions and discontent with institutions or principles. Many conservatives indulge in the former, only radicals in the latter. Again radicalism is not a mere "tearing up by the roots," as the word is commonly interpreted, but is rather, as Philips Brooks writes, "a getting down to the root of things and planting institutions anew on just principles. An enlightened radicalism has regard for righteousness and good government, and will resist all enslavement to old forms and traditions, and will set them aside unless it shall appear that any of these have a radically just and defensible reason for their existence and continuance." Radicalism thrives where conditions are favorable to a change in ideals. It aims to establish new institutions or to propagate new principles, and this presupposes new ideals. As the habits of a man tend to correspond to his ideals, so too the institutions of a nation conform in a broad way to its ideals. In England during the Middle Ages the institutions of the country were strongly influenced by the religious ideal; later on, when the nation's ideal became national glory, they assumed a political character; and now they reflect the dominant influence which the economic ideal has exerted during the past century. The ideals of a people than are bound to undergo changes, and these are sometimes, though not always, for a nation's good. They are developed in the main by an increase in knowledge and by industrial change. Institutions, however, do not keep pace with this advance in ideals; and as a consequence discontent results and radicalism is born. Moreover, institutions are never an adequate expression of the ideal. "Men are never as good as the goodness they know. Institutions reveal the same truth. The margin between what society knows and what it is" makes radicalism possible. In his introduction to _The Revolt of Islam_, Shelley expresses the same thought: "The French Revolution may be considered as one of those manifestations of a general state of feeling among civilized mankind produced by a defect of correspondence between the knowledge existing in society and the improvement or gradual abolition of political institutions." The greater that this defect of correspondence becomes, the more intense will be the radicalism that inevitably ensues. Radicals want a change. The extent of this change differentiates them fairly well among themselves. Some would completely sweep away every existing institution. Thus Shelley thought the great victory would be won if he could exterminate kings and priests at a blow.