“All the political parties alike have their origins in past ideas and not in new ideas — and none more conspicuously so than the Marxists.”
Source: Essays In Biography (1933), Trotsky On England, p. 91
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John Maynard Keynes 122
British economist 1883–1946Related quotes

“All told it is a new world. It calls for new ideas. In Canada it calls for a New Party.”
Source: The New Party - (1961), Chapter 7, Program, p. 83

" Searching for the Next GOP Villain http://www.jewishworldreview.com/0405/sajak041805.php3," in Jewish World Review, April 18, 2005.
2000s
Source: The Age of Reform: from Bryan to F.D.R. (1955), Chapter III, part I, p. 97

1990s, I Am a Man, a Black Man, an American (1998)

“Nothing is more dangerous than an idea, when you have only one idea.”
Propos sur le Religion no. 74 (1938), under the pen name Alain.
Alternate translation: “Nothing is more dangerous than an idea, when it's the only one we have.” IZQuotes https://izquotes.com/quote/%C3%A9mile-chartier/nothing-is-more-dangerous-than-an-idea-when-you-have-only-one-idea-390165 (retrieved 10/30/18).

“The mind, once stretched by a new idea, never returns to its original dimensions.”

“The mind that opens to a new idea, Never comes back to its original size.”
Actually said by Oliver Wendell Holmes, Sr. in his book The Autocrat of the Breakfast Table: "Every now and then a man's mind is stretched by a new idea or sensation, and never shrinks back to its former dimensions."
Misattributed

Essay on the Principle of Population (1798; rev. through 1826)
Source: The Passing of an Illusion, The Idea of Communism in the Twentieth Century (1999), p. 175