Thought, as an intellectual product, can indeed be studied apart from the mind that creates it, and can be treated by history as a material fact subject to the fixed succession of natural laws. But the exclusive use of such a method, at least in any other subject of study than that of the results of physical discovery, must be defective, even independently of the question of the action of free will, unless the thoughts which are the object of study be also connected with the personality of the thinker who produces them. His external biography is generally unimportant, save when the individual character may have impressed itself upon public events; but the internal portraiture, the growth of soul as known by psychological analysis, is the very instrument for understanding the expression of it in life or in literature.(112) It is requisite to know the mental bias of a writer, whether it be practical, imaginative or reflective; to see the _idola specus_ which influenced him, the action of circumstances upon his character, and the reaction of his character upon circumstances; before we can gain the clue to the interpretation of his works. But if we wish further to derive moral instruction from him, the biographical mode of study becomes even more necessary. For the notion of freedom as the ground of responsibility is now superadded; and the story of his life is the sole means for such an apprehension of the causes of his heart-struggles as shall enable us to take the gauge of his moral character, and appropriate the lessons derivable from the study of it.