In Rhetorics of Fantasy Mendlesohn proposes four ways to categorise fantasy fiction, namely:

Portal/quest fantasy or
Immersive fantasy or
Intrusive fantasy or
Liminal fantasy

In portal or quest fantasies, characters leave a familiar home and journey into a new land, typically with the help of a guide who also conveys an absolute and unchallenged history of the land and its world. There is none of the ambiguity of interpretation that we see in real world history.

In immersive fantasy, the world is entirely known to the characters who inhabit and act in it. Immersive fantasy is also characterised by a “thinning” of the world of the protagonists which is under threat and experiencing a decay of some form. Discovery and restoration may be the engine of a portal fantasy, but this threat and thinning drives the immersive fantasy.

In intrusive fantasy, the fantastic or supernatural intrudes into or invades a familiar world (which could be our contemporary world or it could be itself a fantasy environment). The intrusion generates the threat, conflict and change to drive the story forward.

Liminal fantasy is harder to define. The fantasy elements sit at the edge of the story so that neither characters nor reader can be entirely certain that it exists.