“It's all nonsense to say that the Fifteenth Century can't possibly speak to the Twentieth, because it is the Fifteenth and not the Twentieth, and because those two Centuries haven't got a Common Denominator. They have. It's Human Nature.”

Ancient Indian Historical Tradition (1962)

R. G. Collingwood (1937), as cited in: Patrick Suppes (1973), Logic, methodology and philosophy of science: Proceedings.

Humanities interview (1996)
Context: I was very interested in the Great War, as it was called then, because it was the initial twentieth-century shock to European culture. By the time we got to the Second World War, everybody was more or less used to Europe being badly treated and people being killed in multitudes. The Great War introduced those themes to Western culture, and therefore it was an immense intellectual and cultural and social shock.
Robert Sherwood, who used to write speeches for Franklin D. Roosevelt, once noted that the cynicism about the Second War began before the firing of the first shot. By that time, we didn't need to be told by people like Remarque and Siegfried Sassoon how nasty war was. We knew that already, and we just had to pursue it in a sort of controlled despair. It didn't have the ironic shock value of the Great War.
And I chose to write about Britain because America was in that war a very, very little time compared to the British — just a few months, actually. The British were in it for four years, and it virtually destroyed British society.

Wars I Have Seen (1945)

Four Speeches on the Corporate State, Rome, (1935) pp. 39-40. Speech delivered to the workers in Milan. Eric Jabbari, Pierre Laroque and the Welfare State in Postwar France, Oxford University Press, (2012) p. 46
Context: Fascism establishes the real equality of individuals before the nation… the object of the regime in the economic field is to ensure higher social justice for the whole of the Italian people… What does social justice mean? It means work guaranteed, fair wages, decent homes, it means the possibility of continuous evolution and improvement. Nor is this enough. It means that the workers must enter more and more intimately into the productive process and share its necessary discipline… As the past century was the century of capitalist power, the twentieth century is the century of power and glory of labour.

Werner Erhard on L. Ron Hubbard — quoted in [L. Ron Hubbard: Messiah or Madman?, 1987, Bent Corydon and Ronald DeWolf, 15, 0818404442]
Attributed

'Poland. A historical sketch'

What postmodern doesn’t?
Section 9.811 (p. 273)
Flight from Nevèrÿon (1985)

quoted in Advertising Age, Sep. 3, 1976
1970s
Variant: Advertising is the greatest art form of the twentieth century
Context: Advertising is the greatest art form of the twentieth century.