“And the central assertion of his philosophy is that this inner realm is the 'spiritual world' and that once man has learned to enter this realm, he realizes that it is not a mere imaginative reflection of the external world, but a world that possesses its own independent reality.”

As quoted in ‘Interview with J. G. Ballard’, Munich Round Up, 100 (1968), with translation by Dan O’Hara http://www.ballardian.com/munich-round-up-interview-with-jg-ballard <br class="br">Context: I define Inner Space as an imaginary realm in which on the one hand the outer world of reality, and on the other the inner world of the mind meet and merge. Now, in the landscapes of the surrealist painters, for example, one sees the regions of Inner Space; and increasingly I believe that we will encounter in film and literature scenes which are neither solely realistic nor fantastic. In a sense, it will be a movement in the interzone between both spheres.

'Painting and Culture' p. 58
Search for the Real and Other Essays (1948)

Source: Works of Love

Source: Aphorisms and Reflections (1901), p. 89

"Platonic Justice", Ethics, April 1938. Translated by Glenn Negley from "Die platonische Gerechtigkeit," Kantstudien, 1933. (The author corrected the translation in 1957), published in What is Justice? (1957)

1941 - 1967
Source: 'Statements by Four artists', Edward Hopper, in 'Reality' 1., Spring 1953, p. 8

L.A. Cooper and R.N. Shepard (1984). "Turning something over in the mind." Scientific American 251(6), 106-114; p. 114.
Context: In spite of some unresolved issues, the close match we have found between mental rotation and their counterparts in the physical world leads inevitably to speculations about the functions and origin of human spatial imagination. It may not be premature to propose that spatial imagination has evolved as a reflection of the physics and geometry of the external world. The rules that govern structures and motions in the physical world may, over evolutionary history, have been incorporated into human perceptual machinery, giving rise to demonstrable correspondences between mental imagery and its physical analogues.

Anti-Dühring http://www.marxists.org/archive/marx/works/subject/quotes/index.htm (1878)