Originally, a palimpsest was any material – e.g., parchment, a slate – so treated that anything written upon it could be erased, and it could be written upon again. In later usage, the term came to describe any actual material – again e.g., parchment, though not a slate – known to have been written on more than once. In this encyclopedia we use the term in a sense analogous to its original meaning, to refer to what one might call a "writing world" – one which outlives the brief Realities inscribed, each after another, upon it. "Palimpsest" is a term, therefore, perhaps less useful for describing fantasy than Supernatural Fiction, many forms of which tend to postulate higher realities to which this world is subordinate, and which represent an occult lesson for those of us capable of perceiving it (see Theosophy).
But there is a significant fantasy application for the term. The long tradition of serious and cod speculation based on gnostic doctrine (see Gnostic Fantasy) tends to postulate a central and more real world upon which innumerable Shadow worlds are written, erased, and written again; and, although fantasies based on this sort of dualism tend to harbour fossilized supernatural-fiction motifs and assumptions, it seems wise to treat them as more than exercises in Occultism. The novels of John Crowley – whose protagonists are typically caught in the shadows of the mundane world, and who search for the true Story – are fantasies if for no other binding reason than that the truth (in a didactic sense) of the story is of radically less importance than the fact that it is a story, and an autonomous one.
Cosmologies – like the Multiverse created by Michael Moorcock and Roger Zelazny's Amber – which treat huge arrays of mundane and fantasy realities as having been written in sand upon a central and fundamental reality can also be described as treating that substrate as a palimpsest. Though echoes of occult thinking haunt works of this sort, their overriding impulse is toward fantasy outcomes.
Both its origin and its usefulness in describing supernatural fictions give a sense that the term best describes vertical structures, stories in which new realities are written over – on top of – prior realities. When Alternate Realities convene or portals open horizontally – so that there is a "geographical" or lateral mixing of kinds of world – then the term is less useful; in this encyclopedia the term Crosshatch is used to signal lateral mixings. [JC]