Popper, K. R. "Of Clouds and Clocks," in his Objective Knowledge, corrected edition, pp. 206–55, Oxford, Oxford University Press (1973), p. 231 footnote 43, & p. 252; also Popper, K. R. "Natural Selection and the Emergence of Mind", 1977.
„Sir Karl Popper Is Dead at 92. Philosopher of 'Open Society'“. The New York Times. 18 September 1994. ციტირების თარიღი: 15 November 2012. ციტატა: „Sir Karl Popper, a philosopher who was a defender of democratic systems of government, died today in a hospital here. He was 92. He died of complications of cancer, pneumonia and kidney failure, said a manager at the hospital in this London suburb.“