Much has been written about the roots of the mythology created by Tolkien in The Hobbit, The Lord of the Rings, and The Silmarillion. Some of it is insightful -- some of it is superficial. Tom Shippey's work The Road to Middle-Earth lies on the far end of the insightful side of the spectrum. Shippey, was briefly a personal acquaintance of Tolkien. He is a medieval scholar in his own right, having held the Chair of English Language and Medieval Literature at Leeds University (formerly held by Tolkien himself) and the Walter J. Ong Chair of Humanities at St. Louis University in Missouri. His Road to Middle-Earth was first published in 1982, with a second edition in 1992, and a revised and expanded edition in 2003. The subsequent editions are informed by Tolkien's posthumous publications, particularly, the twelve volume set The History of Middle-Earth.
The most important theme in Shippey's work is how philology informed Tolkien's work. Clearly, Tolkien gave enormous attention to the words he chose in all he wrote. His work was deeply informed by his understanding of Old English, Old Norse, and other Northern European medieval languages. Shippey traces a huge number of connections between these languages and Tolkien's writing, and he provides valuable explanations of the significance of specific word choices and invented names to Tolkien's themes and ideas. Shippey's expert analysis reveals layer upon layer of meaning.
Shippey locates Tolkien's legendarium within the myths and legends of Northern Europe in the same way that a philologist might postulate unrecorded words in long dead languages. For example, based on specific observable rules for word relations between languages, the words for dwarves -- "dweorh" (Old English), "dvergr" (Old Norse), and "twerg" (High German) -- allow philologists to postulate "*dvairgs" in Gothic. They may do this despite the absence of any record of the word for dwarves in Gothic. In writing these inferred words, philologists normally precede them with an asterisk, e.g., *dvairgs, to distinguish it from a recorded word.
According to Shippey, philologist, including Tolkien, came to accept this methodology, and to infer -- not just words -- but the realities to which they were attached. He writes, "The whole of their science conditioned them to the acceptance of what one might call '*-' or 'asterisk-reality', that which no longer existed but could with 100 percent certainty be inferred." Furthermore, this methodology encouraged philologists to blur the distinction between historical discovery and creative construction.
Shippey indicates that Tolkien was particular prone to this. Applied to literature, Tolkien called this technique "Sub-Creation." The resulting story lies somewhere between historical reality and mere fiction. Sub-Creation has a depth of meaning and authenticity that reaches beyond the creative product of a single author relying on his or her individual imagination. Shippey's account does much to explain the sense that many Tolkien fans have that Middle-Earth exists on the same plane as the Garden of Eden, Gilgamesh's Cedars of Lebanon, and Asgard of the Aesir. It also explains what Tolkien meant when he wrote that he wanted to create a mythology for England. Middle-Earth is essentially the *Mythology of England.
Despite the strength of Shippey's analysis, one is sometimes left with the feeling that Shippey imputes more than was intended by Tolkien. As a medieval scholar well-equipped with the tools of philology, it would be easy for Shippey to interpret accidental elements in Tolkien's work as part of Tolkien's conscious Sub-Creation; however, even if this is true, it only indicates the extent to which Tolkien was living and breathing the combined mythologies that form the building blocks of Middle-Earth.
The Road to Middle-Earth is loaded with many more insights than I have described here. It is a tour de force of Tolkien scholarship and deserves to be read by every Tolkien fan.