Changes

Popper came to notice the main difference between Marxism, psychoanalytic theory, and Einstein’s theory of relativity, is that a principle of falsifiability is inherent to Einstein’s theory. In contrast, he found that theories like psychoanalysis and Marxism were insusceptible to refutation or experimental falsification. In his view this made theories like these pseudo-scientific, since tests which could falsify them were inconceivable.

Weimar culture and a lineage of philosophers such as Thomas Hobbes, George Berkely, and Wittgenstein, who provided epistemological theories of sense-data, influenced the Vienna Circle’s nominalist and essentialist theories. The logical positivists held metaphysics as meaningless, consisting of nonsensical pseudo-propositions. Popper came to disagree with logical positivist theory and its fundamental claims, such as Rudolph Carnap’s position that probabilities of truth in general synthetic claims could be assessed by calculating the certainty of individual corroborating observations. Popper opposed Carnap’s reductionist position on the verifiability of universal synthetic claims largely on the basis of the Quine-Duhem thesis, which maintains that no individual theory, test, or observation can be separated from the taxonomy of thought which produces it. To Popper, an openness to being refuted by observation, testing, and criticism, was the criteria of demarcation for a claim of scientific value.

== Main Contributions to the Philosophy of Scientific Change ==