The purpose of this book, then, is not to expose the development of Mill's mind, but to explain the nature of his doctrine. It will be a critical essay in the exposition of ideas, not a regurgitation of the Autobiography. Nevertheless, it is necessary to understand not just the doctrine, but the circumstances to which the doctrine was a response. This is a preliminary essential in dealing with all serious writers on moral, political and social questions (though often the material has to be inferred): with Mill it is central to the doctrine itself. There is about Mill at all stages of his intellectual development a sense of historic mission which gives greater confidence than he might have otherwise had, and induces an earnestness of manner deriving from consciousness of obligation to propagate what he conceived to be opinions suitable to the time and point-in-history at which he had arrived. In few nineteenth-century writers (except Marx) is this sense of historic mission as strong as in Mill: in few writers does interpretation of history so completely dominate the fundamental assumptions about the function of philosophical doctrine.