The planetary romance, a story set primarily or wholly on a single planet and illustrating its scenery, native peoples (if any) and cultures, offers considerable scope for science fantasy, in the sense of fantasy rationalized by reference to science-fictional conventions.
David Lindsay's A Voyage to Arcturus, published in 1920 is one of the earliest examples of the type, although it differs from most of them in not assuming a science-fictional background of interplanetary or interstellar travel; it is rather a philosophical romance, which uses an alien planet as a background for exploring philosophical themes. C. S. Lewis' Out of the Silent Planet (1938) is an example of the same type of story, though in its case the preoccupations are theological. In both cases the magical elements are barely rationalized, and in Lewis' case stand in stark contrast to the pseudo-scientific machinery that frames the story.
Some examples of this type of science fantasy deliberately blur the already vague distinction between science fictional paranormal powers and magic; for instance, Poul Anderson's The Queen of Air and Darkness, in which aliens use psionic powers of illusion to imitate earthly myths of fairies—who are themselves traditionally regarded as magical illusionists.
Sword and planet
Many works by Edgar Rice Burroughs fall into this category, as well as those of his imitators such as Otis Adelbert Kline, Kenneth Bulmer, Lin Carter, and John Norman. They are largely classed as "science fantasy" because of the presence of swords and, usually, an archaic aristocratic social system; Burroughs' own novels are, however, skeptical in spirit and almost free of any non-rationalized "fantastic" element (other than the never-explained mechanism by which John Carter gets to Mars).
I've seen them used interchangeably.Was is the actually different between planetary romance and sword & planet genre? Some say they are almost the same and others says they different but what exactly make these genre be name two different genres?