In this book we use this term in three linked and usually easily distinguishable senses.
1. In works such as Too Many Magicians (1967) by Randall Garrett, stock fantasy elements are given a rationale that provides them with internal consistency and coherence. In such works the laws of Magic may be carefully codified, often through the elaborate systems of mysticism found in ritual Alchemy or in the Cabbala, or by using the "laws of magic" devised by Sir James Frazer.
2. Many works appear purely fantastic but then are discovered, usually towards the end, through a foreshadowed or merely tacked-on shift of Perception, to be explicable in mundane terms (i.e., they are rationalized). Much of the Gothic fiction (> Gothic Fantasy) of the late 18th and early 19th centuries, perhaps most typically The Mysteries of Udolpho (1794) by Ann Radcliffe – parodied mercilessly in Northanger Abbey (1818) by Jane Austen (1775-1817) – was rationalized in this way, so that what appeared to be quasi-magical was in fact being stage-managed via elaborate machineries. In modern written fantasy, the explaining-away of the fantastic is comparatively rare, having for the most part been displaced to metafictions and Psychological Thrillers like Theodore Sturgeon's Some of Your Blood (1961). In the movies, this form of RF remained commoner until later – especially in Children's Fantasy movies, where protagonists were very likely to wake and discover "it had all been a Dream" – although the paradigm is an adult movie, The Beast with Five Fingers (1946). Unusually, the wizards in Dave Duncan's The Seventh Sword trilogy (1988) turn out to be masquerading technologists even though the world they inhabit is one in which the Goddess and her magical servants regularly intervene.
3. Much contemporary fantasy turns out to be Science Fantasy, in that the explanations are managed not in terms of the mundane known but in terms of sf tropes. Thus in Julian May's Saga of Pliocene Exile (1981-1984) the Fairies whom the adventurers meet in the past turn out to be aliens, the Vampires in Barbara Hambly's Those who Hunt the Night (1988) have been changed by a virus with which it is possible to experiment in the laboratory, and so on. This sort of rationalized fantasy is often closely allied with, and intermingled with, Revisionist Fantasy and Slipstream. Perhaps the most common version of this is the trope whereby Pariah Elites of Elves or Wiccans turn out to be, in our terms, mutants with psi powers (> Talents).
Sometimes, of course, the rationalization works the other way – genre fantasy has cheerfully naturalized standard sf icons by giving them a magical rationale or attaching their emotional weight to existing fantasy icons. For example, Dragons have acquired many of the characteristics of sf aliens in the course of being subjected to revisionist fantasy; Hambly's dragons in Dragonsbane (1986) have specifically arrived in the magical human world they now inhabit by winged flight from another planet.
Meaning 3 is often back-conflated with the other two, so that, for example, the petrifaction of a troll in Poul Anderson's Three Hearts and Three Lions (1961) is a magical event with scientific consequences in the shape of the radioactivity released when carbon-based molecules change, by atomic fusion, into silicon – and so the Curse associated with a dead troll's treasure is explained away as radiation sickness.
Much rationalized and quasi-rationalized fantasy takes place in Alternate Worlds; these are sometimes versions of the modern USA with magic substituted for technology, as in Robert Heinlein's "Magic Inc." (1940 as "The Devil Makes the Law") and Poul Anderson's Operation Chaos (1971), and sometimes alternate histories in which historical process has favoured magic as much as technology, as in Orson Scott Card's Tales of Alvin Maker, where an extended Cromwellian rule in England has concentrated the magically gifted as a breeding pool in the colonies to which they were deported.
In theory, RF which uses the real to explain away the fantastic is directly opposite to Fantasies of History, which provide fantastic explanations of the real; in practice, various works combine the two. Tim Powers's The Stress of Her Regard (1989) at once provides a fantastic explanation of such phenomena as the tendency of Romantic poets to get TB, the persistence of the Austrian empire in Italy and the name and Rituals of the Carbonari, yet offers that explanation – vampirism – in quasi-sf terms (silicon lifeforms). [RK]