Editing Karl Popper (section)

=== Background to Popper's ideas ===
Popper's rejection of [[Marxism]] during his teenage years left a profound mark on his thought. He had at one point joined a socialist association, and for a few months in 1919 considered himself a [[communist]].<ref name="JarvieMilford2006">{{Cite book |last1=Ian Charles Jarvie |url=https://books.google.com/books?id=w-BEoTj0axoC&pg=PA129 |title=Karl Popper: A Centenary Assessment Volume I |last2=Karl Milford |last3=David W. Miller |publisher=Ashgate Publishing, Ltd. |year=2006 |isbn=978-0-7546-5375-2 |pages=129–}}</ref> Although it is known that Popper worked as an office boy at the communist headquarters, whether or not he ever became a member of the Communist Party is unclear.<ref name="Hacohen2002">{{Cite book |last=Malachi Haim Hacohen |url=https://books.google.com/books?id=3VtHcYGp2pIC&pg=PA81 |title=Karl Popper. The Formative Years. 1902–1945: Politics and Philosophy in Interwar Vienna |date=4 March 2002 |publisher=Cambridge University Press |isbn=978-0-521-89055-7 |page=81}}</ref> During this time he became familiar with the Marxist view of economics, [[class conflict]], and history.{{sfn|Thornton|2015}} Although he quickly became disillusioned with the views expounded by Marxists, his flirtation with the ideology led him to distance himself from those who believed that spilling blood for the sake of a revolution was necessary. He then took the view that when it came to sacrificing human lives, one was to think and act with extreme prudence.

The failure of democratic parties to prevent fascism from taking over Austrian politics in the 1920s and 1930s traumatised Popper. He suffered from the direct consequences of this failure since events after the ''[[Anschluss]]'' (the annexation of [[Austria]] by the [[German Reich]] in 1938) forced him into permanent exile. His most important works in the field of [[social science]]—''[[The Poverty of Historicism]]'' (1944) and ''[[The Open Society and Its Enemies]]'' (1945)—were inspired by his reflection on the events of his time and represented, in a sense, a reaction to the prevalent [[Totalitarianism|totalitarian]] ideologies that then dominated Central European politics. His books defended democratic liberalism as a social and [[political philosophy]]. They also represented extensive critiques of the philosophical presuppositions underpinning all forms of [[totalitarianism]].{{sfn|Thornton|2015}}

Popper believed that there was a contrast between the theories of [[Sigmund Freud]] and [[Alfred Adler]], which he considered non-scientific, and [[Albert Einstein]]'s [[theory of relativity]] which set off the revolution in [[physics]] in the early 20th century. Popper thought that Einstein's theory, as a theory properly grounded in scientific thought and method, was highly "risky", in the sense that it was possible to deduce consequences from it which differed considerably from those of the then-dominant [[Newtonian physics]]; one such prediction, that gravity could deflect light, was verified by [[Arthur Eddington|Eddington's]] [[Eddington experiment|experiments in 1919]].<ref>{{Cite web |title=Gravitational deflection of light – Einstein Online |url=http://www.einstein-online.info/spotlights/light_deflection.html |url-status=dead |archive-url=https://web.archive.org/web/20191121113731/http://www.einstein-online.info/spotlights/light_deflection.html |archive-date=21 November 2019 |access-date=31 May 2019 |website=www.einstein-online.info}}</ref> In contrast he thought that nothing could, even in principle, falsify psychoanalytic theories. He thus came to the conclusion that they had more in common with primitive myths than with genuine science.{{sfn|Thornton|2015}}

This led Popper to conclude that what was regarded as the remarkable strengths of psychoanalytical theories were actually their weaknesses. Psychoanalytical theories were crafted in a way that made them able to refute any criticism and to give an explanation for every possible form of human behaviour. The nature of such theories made it impossible for any criticism or experiment—even in principle—to show them to be false.{{sfn|Thornton|2015}} When Popper later tackled the [[Demarcation problem|problem of demarcation]] in the philosophy of science, this conclusion led him to posit that the strength of a scientific theory lies in its both being susceptible to falsification, and not actually being falsified by criticism made of it. He considered that if a theory cannot, in principle, be falsified by criticism, it is not a scientific theory.<ref>One of the severest critics of Popper's so-called demarcation thesis was [[Adolf Grünbaum]], cf. ''Is Falsifiability the Touchstone of Scientific Rationality?'' (1976), and ''The Degeneration of Popper's Theory of Demarcation'' (1989), both in his ''Collected Works'' (edited by Thomas Kupka), vol. I, New York: Oxford University Press 2013, ch. 1 (pp. 9–42) & ch. 2 (pp. 43–61).</ref>