Many people throughout the world "inhabit" imaginary worlds communally and persistently, parsing Harry Potter and exploring online universes. These activities might seem irresponsibly escapist, but history tells another story. Beginning in the late nineteenth century, when Sherlock Holmes became the world's first "virtual reality" character, readers began to colonize imaginary worlds, debating serious issues and viewing reality in provisional, "as if" terms rather than through essentialist, "just so" perspectives. From Lovecraft's Cthulhu Mythos and Tolkien's Middle-earth to the World of...