Thus scientific history may go back to the accidents, or events, which traditional history collected for literary reasons, because they struck the imagination, and employ them for the study of evolution. We may thus look for the facts which have influenced the evolution of each one of the habits of humanity. Each event will be arranged under its date in the evolution which it is supposed to have influenced. It will then suffice to bring together the events of every kind, and to arrange them in chronological and geographical order, to have a representation of historical evolution as a whole. Then, over and above the _special_ histories in which the facts are arranged under purely abstract categories (art, religion, private life, political institutions), we shall have constructed a concrete _general_ history, which will connect together the various special histories by exhibiting the main stream of evolution which has dominated all the special evolutions. None of the species of facts which we study apart (religion, art, law, constitutions) forms a closed world within which evolution takes place in obedience to a kind of internal impulse, as specialists are prone to imagine. The evolution of a usage or of an institution (language, religion, church, state) is only a metaphor; a usage is an abstraction, abstractions do not evolve; it is only _existences_ that evolve, in the strict sense of the word.[196] When a change takes place in a usage, this means that the men who practise it have changed. Now, men are not built in water-tight compartments (religious, juridical, economic) within which phenomena can occur in isolation; an event which modifies the condition of a man changes his habits in a great variety of respects. The invasion of the Barbarians influenced alike language, private life, and political institutions. We cannot, therefore, understand evolution by confining ourselves to a special branch of history; the specialist, even for the purpose of writing the complete history of his own branch, must look beyond the confines of his own subject into the field of general events. It is the merit of Taine to have asserted, with reference to English literature, that literary evolution depends, not on literary events, but on facts of a general character.