“Love is a simple thing and a deep thing: it is an act of life and not an illusion. Art is an illusion.”

Daniel Buren, Olivier Mosset, Michel Parmentier and Niele Toroni, at the Paris Biennale in October 1967. Translated and cited in: Lucy R. Lippard, Six Years: The Dematerialization of the Art Object from 1966 to 1972, New York: Praeger, (1973), p. 30.
1960s

Make Your Own 3D Illusions (2014).
Context: We long for a technological world, while keeping the natural aspect of our environment; we want the progress, while maintaining the traditions; we want organization while preserving individual freedom; we produce at a large scale while looking for unique products; we want clearness in our relationships, while we like to play with the ambiguity; we wish everlasting happiness while seeking incomparable magic moments… In reality, from all these contradictions, we are looking for only one thing: ASTONISHMENT. We would life to astonish us every day! That’s why we all, human beings, love playing, because games are synonymous of risk and astonishment. Games are enactments, and the act of playing is an illusion of the illusion of the reality.

"Queen of the Black Coast" (1934)
Source: Conan the Barbarian Omnibus -The Original Stories
Context: He shrugged his shoulders. "I have known many gods. He who denies them is as blind as he who trusts them too deeply. I seek not beyond death. It may be the blackness averred by the Nemedian skeptics, or Crom's realm of ice and cloud, or the snowy plains and vaulted halls of the Nordheimer's Valhalla. I know not, nor do I care. Let me live deep while I live; let me know the rich juices of red meat and stinging wine on my palate, the hot embrace of white arms, the mad exultation of battle when the blue blades flame and crimson, and I am content. Let teachers and priests and philosophers brood over questions of reality and illusion. I know this: if life is illusion, then I am no less an illusion, and being thus, the illusion is real to me. I live, I burn with life, I love, I slay, and am content."

As quoted in Famous Actors and Actresses on the American Stage (1975) by William C. Young, p. 885
Context: Acting is illusion, as much illusion as magic is — and not so much a matter of being real. I mean, I would probably shock Lee Strasberg.

Source: Christie Johnstone (1853), CHAPTER XII.

The Harsh Voice: Four Short Novels (1935)

Source: 2010s, Waking Up (2014), p. 54

Source: Thus Spoke Zarathustra

X magazine (1959-62)
Context: The interesting thing is what happens in the specific picture: its precision in terms of the sensations it produces — the illusion it creates and the effect of this illusion on the psychology opposed to it. General philosophical and technical information however interesting in itself is secondary to this reality.