Daily Close-up, after the Flag, Roberta Brandes Gratz, New York Post, 30 December 1970, p. 25
1970s
“In discussing his work [the art of Marcel Duchamp, ] it is necessary to avoid overrating his silence. I hold him in a very high esteem, but I have to reject his silence. Duchamp was simply finished. He had run out of ideas; he was unable to come up with anything important… I would say that even the bourgeois tendencies in Duchamp's work – i. e., a form of provocative, bohemian behavior intended to 'épater le bourgeois'- follow the same path. Duchamp started out from here and wanted to shock the bourgeoisie, and because of that he destroyed his creative powers… The content of Duchamp's silence refers to the aim of leaving the subconscious passive, of developing it. This is the aspect of Duchamp, which is related to Surrealism. The surrealists asserted that they could live with their subconscious; they thought they were above reality, but instead they were beneath it. They thought they could fish in muddy waters…. but to my mind, the images which emerged have a repressive effect.”
Quote in an interview with , 1986; republished in: Joseph Beuys, Carin Kuoni. Joseph Beuys in America: Energy Plan for the Western Man. New York, 1993.pp. 169-170
Beuys refers in his quote to the so-called 'Silence of Marcel Duchamp', the period that Duchamp stopped creating art
1980's
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Joseph Beuys 50
German visual artist 1921–1986Related quotes

1930s - 1950s, Statement from Modern Painting and Sculpture', (1933)
Source: en.wikiquote.org - Alexander Calder / Quotes of Alexander Calder / 1930s - 1950s / Statement from Modern Painting and Sculpture', (1933)

Source: Art is no longer justifiable or setting the record straight, 2000, p. 66

Charlotte Higgins, "It was 37 years ago today – and Sgt Pepper cover has still failed to pay", http://www.guardian.co.uk/thebeatles/story/0,,1230411,00.html The Guardian, 2004-06-03
On his painting, Marcel Duchamp's World Tour.
Art

as quoted in Joseph Beuys and the Celtic Wor(l)d: A Language of Healing, by Victoria Walters, LIT Verlag Münster, 2012, p. 206
Quotes after 1984, posthumous published
Source: "Anselm Kiefer and the Philosophy of Martin Heidegger" Matthew Biro, Cambridge University Press 1998, p. 304

Quote from: 'Interview with Achille Bonito Oliva', 1986; Republished in: 'Joseph Beuys', Carin Kuoni. Joseph Beuys in America: Energy Plan for the Western Man. New York, 1993
posthumous

Quote from: Entretiens avec Marcel Duchamp, 1965; as cited in Futurism, ed. By Didier Ottinger; Centre Pompidou / 5 Continents Editions, Milan, 2008, p. 198
Duchamp's quote is referring to his painting 'Moulin a café', 1911 - many times reproduced from the lithography, made for the 1947 re-edition of Gleizes and Metzingers book 'Du Cubisme'
1951 - 1968