In many systematizations of Magic its effects are on characters' perceptions rather than the real world: its workings are Illusion. Anodos in George MacDonald's Phantastes (1858), when influenced by a Shadow, sees people and places as uglier and cruder than before, which may or may not be a true insight. A woman's Ghost in Charles Williams's All Hallows Eve (1945) wanders an eerie London which to her seems empty, for she cannot perceive the living. Characters' varying perceptions of the eponymous something in Fritz Leiber's "A Bit of the Dark World" (1962) emphasize its inherent Wrongness. The villain of Graham Dunstan Martin's The Soul Master (1984) controls his slave army by Possession, but lacks a full perception of the world: in an effective metaphor, his slaves are not only unable to see places within the resulting "gaps" but cannot exist in them, seeming to teleport instantly across the unknown regions.
More interestingly, it could be argued that, if Fantasy (and debatably the literature of the Fantastic as a whole) has a purpose other than to entertain, it is to show readers how to perceive; an extension of the argument is that fantasy may try to alter readers' perception of Reality. Of course, quack Religions (etc.) make similar attempts, but a major difference is that, while the latter attempt to convert people to their codified way of thinking, the best fantasy introduces its readers into a Playground of rethought perception, where there are no restrictions other than those of the human imagination. In some modes of the fantastic – e.g., Magic Realism and Surrealism – the attempt to alter the reader's perception is overt, but most full-fantasy texts have at their core the urge to change the reader; that is, full fantasy is by definition a subversive literary form. This also in part explains why there is such a smooth continuum between written fantasy and Fantasy Art.
Other overt examples are particularly noteworthy in fantasy Cinema: Dick Tracy (1990) forces us to perceive its world as if we were living in a Comic strip; Wings of Desire (1987) makes us see our surroundings as an Angel might; The Brave Little Toaster (1987) makes us see electrical appliances as people like us, whereas human beings become potential Gods and thus mere appendages to the real world (the movie uses further perceptual devices: whenever a human looks at a gadget it is suddenly nothing more than a piece of machinery); Jan Švankmajer's Faust (1994) toys with our perceptions to the extent that for hours after any viewing it is hard to cling on to the laws of daily logic. Countless other movies could be cited, but such effects are certainly not confined to the movies: for example, in M John Harrison's A Storm of Wings (1980 US) we are forced to perceive events from alternating viewpoints, alien and human; in Alan Garner's The Owl Service the relic of Blodeuwedd may be an owl or an array of flowers; in John Barth's The Last Voyage of Somebody the Sailor (1992) it is left gloriously unclear as to which memory-string represents true history.
Further aspects of perception are important in fantasy. Three can be described together, when deployed, as "the Fantasy of Perception". The first, and probably the least interesting, is typified by the Rationalized Fantasy, wherein the author knows what is going on but the reader does not – that is, the author plays narrative tricks to mislead our perception of events. An example of this being done quite well is the movie The Beast with Five Fingers (1946), where at the end it is revealed that we have been watching events – notably an amputated hand wreaking Vengeance – through the eyes of the insane murderer.
This example melds neatly into another variant of the fantasy of perception, in which not only the reader but the protagonist misperceives the Story, so that there are sudden reversals of understanding. At its crassest, this is represented by the "I awoke and found that it had all been just a Dream" tale, but there are many more sophisticated manipulations, as in John Fowles's The Magus (1965), where a young man is the victim (as are we) of a carefully constructed Godgame, and the movie Rosemary's Baby (1968), which can be read as the tale of Rosemary's gross misperception of her predicament – she is being possessed (to use the term loosely) all right, but perhaps merely by her new sexual experiences rather than by the offspring of the Devil, with all else being a quasi-hallucinatory by-product. (Ira Levin's original Rosemary's Baby  was less effective in this respect.) A similar reading is overwhelmingly possible for Barton Fink (1990): in such terms, Barton is indeed transported into an alien landscape when he is brought to Hollywood, and his exaggerated perception of its alienness is a self-feeding cause, symptom and result of his mental decline. In William Goldman's Magic (both book  and movie ) the ventriloquist dummy is independently intelligent because Corky perceives it as such – which is precisely why the tale is one of nightmare. In Terry Gilliam's The Fisher King (1991) the protagonist eventually finds the fantastication more rational than the rational. Gene Wolfe's There Are Doors (1988) can be read as an Alternate-World/Alternate-Reality fantasy, but it can equally well stand as a novel in which the narrator is constantly being deluded (or is deluding himself) about what is happening to him. In Donna Tartt's The Secret History (1992) events are so misinterpreted by the narrator that the past becomes unsure to both him and us. In Theodore Sturgeon's tour de force of perceptual shifts, "To Here and the Easel" (1954), the reader soon sees that the frustrated artist in the mundane USA and the imprisoned Knight in the setting of Ariosto's Orlando Furioso (1516) are the same protagonist, the fantasy obstacles being perceptual metaphors for a Reality he cannot bear; the same interpretation of an apparent Secondary World is indicated in William Mayne's A Game of Dark (1971). The impact of "The Turn of the Screw" (1898) by Henry James – filmed as The Innocents (1961; vt The Turn of the Screw) – derives from the fact that we do not know if the governess's perception of Ghosts is valid, or even if her belief that the now-dead couple's love affair psychologically scarred the children is justified.
All of the above examples play with our (and their protagonists') perception, but the Gilliam movie and the Wolfe novel take matters further: it becomes easier to believe the fantasy version of events than the rationalization (> Rationalized Fantasy) that is on offer. Both the protagonists and ourselves experience a perceptual shift (again, this relates to the notion of fantasy as a deliberately perception-changing literature). Sometimes this can be right on the surface – for example, in Hook (1991) the ageing Peter Pan has retained his realist perception throughout the voyage to Neverland and the discovery of all its strangenesses, so that when the Lost Boys invite him to join their feast he sees only empty plates; the turning-point of the movie comes when his perception shifts such that he can see the food – a moment of Recognition. Perceptual shifts are the key to sf's conceptual breakthrough, when suddenly a new "truth" is revealed to both protagonist and reader; more profoundly, in – for example – a Slingshot Ending, no new "truth" is directly revealed, only that the old "truth" was a simplification or outright falsity, so that the interaction between reader and text is such that the reader's imagination spirals away into new worlds of perception that, in the end result, may have only a remote relationship to the original text. This need not occur at the end of the text – it need not be a sort of open-ended "twist in the tail". Overall, the most significant piece of fantastication in Gilliam's The Adventures of Baron Munchausen (1989) is that it forces us into a whole string of perceptual shifts, notably concerning the venue in which events are actually occurring: On a stage? In "reality"? Inside the head of the Baron, a territory into which the child (with us in tow) can gain admission? Inside the head of the fascinated child?
A further (minor) issue of perception relates to critical analysis. For example, many of the novels of Sheri S Tepper – such as the series begun with Grass (1989) – can be read with equal validity as sf or as fantasy set in sf contexts. Such differences of perception are significant, however, mainly only to critics and to publishers' sales department: an intelligent author like Tepper has her own conceptual and philosophical agenda, so that categorization is unimportant, and her readers presumably have a similar attitude. [JG/DRL]