Without some knowledge of Constitutional History it is absolutely impossible to do justice to the characters and positions of the actors in the great drama; absolutely impossible to understand the origin of parties, the development of principles, the growth of nations in spite of parties and in defiance of principles. It alone can teach why it is that in politics good men do not always think alike, that the worst cause has often been illustrated with the most heroic virtue, and that the world owes some of its greatest debts to men from whose very memory it recoils.
The Constitutional History of England (1873-8; Oxford: Clarendon Press, 1903) vol. 1, pp. iii-iv.