Fantasy is not so much a mansion as a row of terraced houses, such as the one that entranced us in C. S. Lewis's The Magician's Nephew with its connecting attics, each with a door that leads into another world. There are shared walls, and a certain level of consensus around the basic bricks, but the internal décor can differ wildly, and the lives lived in these terraced houses are discrete yet overheard.

Fantasy literature has proven tremendously difficult to pin down. The major theorists in the field – Tzvetan Todorov, Rosemary Jackson, Kathryn Hume, W. R. Irwin and Colin Manlove – all agree that fantasy is about the construction of the impossible whereas science fiction may be about the unlikely, but is grounded in the scientifically possible. But from there these critics quickly depart, each to generate definitions of fantasy which include the texts that they value and exclude most of what general readers think of as fantasy. Most of them consider primarily texts of the nineteenth and early twentieth century. If we turn to twentieth-century fantasy, and in particular the commercially successful fantasy of the second half of the twentieth century, then, after Tolkien's classic essay, ‘On Fairy Stories’, the most valuable theoretical text for taking a definition of fantasy beyond preference and intuition is Brian Attebery's Strategies of Fantasy (1992). Building on his earlier book, The American Fantasy Tradition (1980), Attebery proposed that we view fantasy as a group of texts that share, to a greater degree or other, a cluster of common tropes which may be objects but which may also be narrative techniques.