“The time has probably come to admit that the notion of an avant-garde is no longer useful in discussing contemporary literature. How can there be an avant-garde without a mainstream? Avant-garde de quoi? one must ask. Establishment institutions — universities, museums, foundations, commercial galleries, even the state — have embraced the idea of experimental art for so long that the avant-garde is now a safely domesticated concept, just another traditional style.”

"Reconsidering the Spiritual in Art" http://www.blackbird.vcu.edu/v2n1/gallery/kuspit_d/reconsidering_print.htm, Blackbird (2003).

The Elegant Universe : Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory (1999), p. 271
Context: Physicists are more like avant-garde composers, willing to bend traditional rules and brush the edge of acceptability in the search for solutions. Mathematicians are more like classical composers, typically working within a much tighter framework, reluctant to go to the next step until all previous ones have been established with due rigor. Each approach has its advantages as well as drawbacks; each provides a unique outlet for creative discovery. Like modern and classical music, it’s not that one approach is right and the other wrong – the methods one chooses to use are largely a matter of taste and training.

Letter to A.S. Suvorin (May 14, 1889)
Letters

"Avant-Garde and Kitsch" http://www.sharecom.ca/greenberg/kitsch.html (1939), p. 19
1960s, Art and Culture: Critical Essays, (1961)

A Voice from the Attic (1960)

Introduction : The absurdity of the Absurd
The Theatre of the Absurd (1961)
Context: The "poetic avant-garde" relies on fantasy and dream reality as much as the Theatre of the Absurd does; it also disregards such traditional axioms as that of the basic unity and consistency of each character or the need for a plot. Yet basically the "poetic avant-garde" represents a different mood; it is more lyrical, and far less violent and grotesque. Even more important is its different attitude toward language: the "poetic avant-garde" relies to a far greater extent on consciously "poetic" speech; it aspires to plays that are in effect poems, images composed of a rich web of verbal associations.
The Theatre of the Absurd, on the other hand, tends toward a radical devaluation of language, toward a poetry that is to emerge from the concrete and objectified images of the stage itself. The element of language still plays an important part in this conception, but what happens on the stage transcends, and often contradicts, the words spoken by the characters. In Ionesco's The Chairs, for example, the poetic content of a powerfully poetic play does not lie in the banal words that are uttered but in the fact that they are spoken to an ever-growing number of empty chairs.

Jeff Koons in: Graeme Green. " 60 SECONDS: Jeff Koons http://metro.co.uk/2007/07/18/60-seconds-jeff-koons-532798/#ixzz3bThr2XKI," at metro.co.uk, 2007/07/18
1990s and later

On tax-funded art: National Endowment for the Arts v. Finley (1998) (concurring).
1990s

Source: Sculpting in Time (1986), p. 97