[We] have in The Hobbit and its sequel what is in fact the same story, told first very simply, and then again, very intricately. Both works have the same theme, a quest on which a most unheroic hobbit achieves heroic stature; they have the same structure, the "there and back again" of the quest romance, and both extend the quest through the cycle of one year, The Hobbit from spring to spring, the Rings from fall to fall.

The episodic structures of the two books are so closely parallel one says without exaggeration that The Lord of the Rings is The Hobbit writ large. (p. 21)

But if The Hobbit and The Lord of the Rings are in essence the "same book," why did Tolkien feel obliged to write again what he had already done once? The answer is, of course, that far from being the same book, they...