Designed in part to substantiate Wolfe's definition of science fantasy as ‘a science fiction story told with the outlook, the flavour of fantasy’, The Urth Cycle is a slyly deceptive conflation of these two frequently discrete genres. While this definition is ambiguous, it seems to suggest that Wolfe is hybridising fantasy's employment of a magical force (as described by Ann Swinfen), which is closed to rational or pseudo-rational explanation, with science fiction's appeal to the rational (observed by, for example, Warren W. Wagar).

Brian Attebery remarks on the integration of the genres’ contrary rational and non-rational discourses when he posits:

In Attebery's terminology, The Urth Cycle is a ‘rationalised fantasy’, wherein ‘the apparent magic is explained away at the end of the story’, or can be ‘explained away’ if the reader apprehends the clues that Wolfe provides.

For example, the feast at which Thecla is consumed by Vodalus's rebels in The Claw of the Conciliator seems to mark the point at which her soul is mystically amalgamated with Severian's. However, the banquet initiates something far more mundane. Although the feast shares religious parallels with the Roman Catholic Mass, with Saint Symeon the Younger's observation that ‘The One who has become many, remains the One undivided, but each part is all of Christ’, and with the apocryphal Gospel of Eve (‘I am thou and thou art I; and wheresoever thou mayest be I am there. In all I am scattered, and whensoever thou willest, Thou gatherest me; and gathering me thou gatherest thyself’), such allusions are misleading.

If these connotations are excluded, it becomes clear that Severian's progression from the one into the manifold (the Autarch) is not the result of a series of mystical unions but a consequence of an entirely chemical assimilation.