“All metaphysical theories are inconclusively vulnerable to positivist attack.”
Source: Sartre: Romantic Rationalist (1953), Ch. 9, p. 127
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Iris Murdoch 61
British writer and philosopher 1919–1999Related quotes

Ch 11. "The Demarcation between Science and Metaphysics." (Summary, p. 253)
Conjectures and Refutations: The Growth of Scientific Knowledge (1963)

“Darwinism is not a testable scientific theory, but a metaphysical research program.”
Unsourced variant: Evolution is not a fact. Evolution doesn't even qualify as a theory or as a hypothesis. It is a metaphysical research program, and it is not really testable science.
Popper later retracted his criticisms:
I have changed my mind about the testability and logical status of the theory of natural selection; and I am glad to have an opportunity to make a recantation.
:* "Natural selection and the emergence of mind" dialectica http://www.dialectica.ch/ Vol. 32 (1978), p. 339-355; republished in Evolutionary Epistemology, Rationality, and the Sociology of Knowledge (1987) edited by Gerard Radnitzky and W. W. Bartley, III
Unended Quest: An Intellectual Autobiography (1976)

Selected works, The Savage Anomaly: The Power of Spinoza's Metaphysics and Politics (1991)

Notice sur les Titres et Travaux scientifiques de Pierre Duhem rédigée par lui-même lors de sa candidature à l'Académie des sciences (mai 1913), The Aim and Structure of Physical Theory (1906)

Dept. of Govt. Affairs (15 August 1960).
Scientology Policy Letters

Source: The End of Science (1996), p. 27

Source: Introduction to semantics, 1962, p. 80-81