“All the stories are fictions. What matters is which fiction you believe.”

Source: 1880s, Personal Memoirs of General U. S. Grant (1885), Ch. 67.

Interview with Weird Tales (24 May 2007) http://weirdtales.net/wordpress/2007/05/24/george-rr-martin-on-magic-vs-science/
Context: I think that for science fiction, fantasy, and even horror to some extent, the differences are skin-deep. I know there are elements in the field, particularly in science fiction, who feel that the differences are very profound, but I do not agree with that analysis. I think for me it is a matter of the furnishings. An elf or an alien may in some ways fulfill the same function, as a literary trope. It’s almost a matter of flavor. The ice cream can be chocolate or it can be strawberry, but it’s still ice cream. The real difference, to my mind, is between romantic fiction, which all these genres are a part of, and mimetic fiction, or naturalistic fiction.

Source: Lord of Shadows

Source: Iranian Students News Agency, 2004 http://www.isna.ir/news/8307-08004/%D9%85%D8%AF%D9%8A%D8%A7-%D9%83%D8%A7%D8%B4%D9%8A%DA%AF%D8%B1-%D9%82%D8%B1%D8%A7%D8%B1-%D8%A8%D8%B1-%D8%A7%D9%8A%D9%86-%D9%86%D9%8A%D8%B3%D8%AA-%D9%83%D9%87-%D8%AA%D9%88%D8%B3%D8%B7-%D9%86%D9%88%D9%8A%D8%B3%D9%86%D8%AF%DA%AF%D8%A7%D9%86-%D8%A7%D9%8A%D8%B1%D8%A7%D9%86%D9%8A-%D8%B4%D8%A7%D9%87%D9%83%D8%A7%D8%B1

"My Own View" in The Encyclopedia of Science Fiction (1978) edited by Robert Holdstock; later published in Asimov on Science Fiction (1981)
General sources

and it goes from there.
Vanna Bonta Talks About Quantum fiction: Author Interview (2007)

Robot Dreams (1986), introduction
General sources

As quoted in The Issue at Hand: Studies in Contemporary Magazine Science Fiction (1964) by James Blish, p. 14