“The assumption that anything true is knowable is the grandfather of paradoxes.”
Source: Labyrinths of Reason (1988), Chapter 12: "Omniscience", p. 260
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William Poundstone 33
American writer 1955Related quotes
Source: The Four Pillars of Investing (2002), Chapter 2, Measuring The Beast, p. 53.

“Igor: My grandfather used to work for your grandfather. Of course the rates have gone up.”
Young Frankenstein

Source: Mysteries (1978), p. 125
Context: No matter how honest scientists think they are, they are still influenced by various unconscious assumptions that prevent them from attaining true objectivity. Expressed in a sentence, Fort's principle goes something like this: People with a psychological need to believe in marvels are no more prejudiced and gullible than people with a psychological need not to believe in marvels.

“Anything is true, is essential to the national.”
in Greek: "Εθνικόν το Αληθές"
Thoughts of the poet, prolegomena by Iakovos Polylas, "Poems, Icarus edition, 1961"

“Anything is true if enough people believe it is.”
"Half-Lives: The First Luisa Rey Mystery", p. 99
Cloud Atlas (2004), Half-Lives: The First Luisa Rey Mystery (Part 1)

“Study the assumptions behind your actions. Then study the assumptions behind your assumptions.”
Source: Learning How to Learn: Psychology and Spirituality in the Sufi Way