A perfect historian must possess an imagination sufficiently powerful to make his narrative affecting and picturesque; yet he must control it so absolutely as to content himself with the materials which he finds, and to refrain from supplying deficiencies by additions of his own. He must be a profound and ingenious reasoner; yet he must possess sufficient self-command to abstain from casting his facts in the mould of his hypothesis.

Critical and Miscellaneous Essays (ed. 1841)