"Every preface," says William Smellie at the start of his preface to The Philosophy of Natural History published in Edinbugh in 1790, "Every preface, besides occasional and explanatory remarks, should contain not only the general design of the work, but the motives and circumstances which led the author to write on that particular subject. If this plan had been universally observed, a collection of prefaces would have exhibited a short, but curious and useful history of both literature and authors. "
This plan was never universally observed but it has been widely observed. Saint John starts his life of Jesus with a preface on the nature of speech and godhead. Five of Shakespeare's plays have prologues spoken straight to the audience. Few great writers have not placed before one of their books a verbal doorstep to help readers leave the ground they usually walk on and allow them a glimpse of the interior. Prefaces are advertisements and challenges. They usually indicate the kind of reader the book was written to please, the kind of satisfaction it aims to give.
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