Although history and biography both relate to the affairs of men, and are employed in the narrative of human events, they are governed by opposite principles, and require, for their successful prosecution, different powers and habits of thought. The main object of history is the tracing out the growth of nations, the great events which lead to their rise or fall, the causes operating on the social body, which at one period conduct to power and greatness, at another induce weakness and decay. Biography is concerned with individual life. Its aim is to trace the annals, not of nations, but of persons; to portray, not the working of general causes on the progress of empires, but the influence of particular characters on their most interesting episodes. The former requires habits of general thought, and the power of tracing one common principle through a great variety of complicated details; the latter, close attention to individual incidents, and a minute examination of the secret springs of human conduct. The first is closely allied to the generalisations of the philosopher; the latter requires the powers of the dramatist. The two branches of composition, however, are nearly allied, and frequently run into each other. History generally finds its most interesting episodes, often its most important subjects, in the narrative of individual greatness; biography is imperfect unless, in addition to tracing the achievements of the individuals it records, it explains their influence upon the society among whom they arose.