In logic, anti-psychologism (also logical objectivism or logical realism) is a theory about the nature of logical truth, that it does not depend upon the contents of human ideas but exists independent of human ideas.
The concept of anti-psychologism was further developed by Gottlob Frege (the most famous anti-psychologist of logic), and has been the centre of an important debate in early phenomenology and analytical philosophy.
The psychologism dispute (German: Psychologismusstreit) in 19th-century German-speaking philosophy is closely related to the contemporary internalism and externalism debate in epistemology; psychologism is often construed as a kind of internalism (the thesis that no fact about the world can provide reasons for action independently of desires and beliefs) and anti-psychologism as a kind of externalism (the thesis that reasons are to be identified with objective features of the world).
Edmund Husserl was another important proponent of anti-psychologism, and this trait passed on to other phenomenologists, such as Martin Heidegger, whose doctoral thesis was meant to be a refutation of psychologism. They shared the argument that, because the proposition "no-p is a not-p" is not logically equivalent to "It is thought that 'no-p is a not-p'", psychologism does not logically stand. Psychologism was criticized in logic also by Charles Sanders Peirce whose fields included logic, philosophy, and experimental psychology, and generally in philosophy by Maurice Merleau-Ponty who held the chairs of philosophy and child psychology at the University of Paris.
Psychologism is not widely held amongst logicians today, but it does have some high-profile defenders, for example Dov Gabbay.
- Dermot Moran, Rodney K. B. Parker (eds.), Studia Phaenomenologica: Vol. XV / 2015 – Early Phenomenology, Zeta Books, 2016, p. 75: "Husserl was an exponent of logical objectivism and an opponent of logical psychologism".
- Edgar Morscher (1972), "Von Bolzano zu Meinong: Zur Geschichte des logischen Realismus." In: Rudolf Haller (ed.), Jenseits von Sein und Nichtsein: Beiträge zur Meinong-Forschung, Graz, pp. 69–102.
- Penelope Rush, "Logical Realism", in: Penelope Rush (ed.), The Metaphysics of Logic, Cambridge University Press, 2014, pp. 13–31.
- Bernard Bolzano (Stanford Encyclopedia of Philosophy); Routledge Encyclopedia of Philosophy (1998): "Ryle, Gilbert (1900-76)."
- William R. Woodward, Hermann Lotze: An Intellectual Biography, Cambridge University Press, 2015, pp. 74–5.
- Sullivan, David. "Hermann Lotze". In Zalta, Edward N. Stanford Encyclopedia of Philosophy.
- Matthias Rath, Der Psychologismusstreit in der deutschen Philosophie, 1994
- Giuseppina D'Oro, "Collingwood, psychologism and internalism," European Journal of Philosophy 12(2):163–177 (2004): "internalism is often associated with psychologism".
- Psychologism (Stanford Encyclopedia of Philosophy): "Examples of Psychologistic Reasoning"
- Peirce attacked the idea, held by some logicians at that time, that rationality rests on a feeling of logicality, rather than on fact. See the first of Peirce's 1903 Lowell Institute Lectures "What Makes a Reasoning Sound?", Essential Peirce v. 2, pp. 242-257. See also the portion of Peirce's 1902 Minute Logic published in Collected Papers v. 2 (1931), paragraphs 18–19 and 39–43. Peirce held that mathematical and philosophical logics precede psychology as a special science and that they do not depend on it for principles.
- Peirce (sometimes with Joseph Jastrow) investigated the probability judgments of experimental subjects, pioneering decision analysis. He and Jastrow wrote "On Small Differences in Sensation", Memoirs of the National Academy of Sciences (1885), 3, 73-83, presented 17 October 1884, reprinted in Collected Papers v. 7, paragraphs 21–35. Classics in the History of Psychology. Eprint.
- Reynolds, Jack (as last updated 2005), "Maurice Merleau-Ponty (1908–1961)", Internet Encyclopedia of Philosophy. Eprint.
- Vladimir Bryushinkin. Metapsychologism in the Philosophy of Logic. Proc. Logic and Philosophy of Logic, 20th World Congress in Philosophy, 2000.
- Dov Gabbay and John Woods. The New Logic. In Journal of the Interest Group in Pure and Applied Logic, Volume 9(2). Oxford, 2000.