OBJECTIVITY, RATIONALITY, AND THE THIRD WORLD: JUSTIFICATION AND THE GROUNDS OF PSYCHOLOGISM

What is psychologism? What are its grounds? And why have so many philosophers been opposed to it? This dissertation addresses these questions through an analysis of the anti-psychologistic arguments that appear in the logical and epistemological writings of Gottlob Frege and Karl Popper. Psychologism emerges in each of these contexts as the thesis that statements can be justified by sense perceptions. As such, it has traditionally been associated with subjectivism, relativism, and other attempts to ground knowledge on something not rational in character.;Frege and Popper each opposed psychologism with the introduction of a third realm to insure the possibility of objective knowledge and objective standards for rationality. But owing to what I call an "epistemological paradigm shift," these terms--"objectivity", "rationality", and "third realm"--have different senses for Popper and Frege. Despite normal similarities, Fregean and Popperian anti-psychologisms are distinct and epistemologically opposed positions.;Frege's opposition to psychologism insisted upon the necessity of a priori valid statements for justification, and hence objective knowledge. Here, rationality was equated with logical justification. And to that extent, I argue that Frege's anti-psychologism was meant to oppose fallibilism in logic and mathematics. But Popper's epistemology forsakes both a priori valid statements and the justified true belief theory of knowledge. Here, rationality is equated not with logical justification, but with logical criticism. And Popper's fallibilistic anti-psychologism can be seen as a lemma in his general argument against the possibility of rational justification: statements cannot be justified logically, and psychological justification won't do either!;These epistemological differences are also reflected in different characterizations of the third realm. Whereas Frege construed third realm objects as eternal and immutable, completely independent of the human mind, Popper regards them as human creations. At base in this dispute is the question whether human knowledge is created or discovered. And here one can glean very real differences in attitude concerning cognitive authority. Whereas Frege's anti-psychologism proceeded from the recognition of the cognitive authority of classical logic and mathematics, Popper's anti-psychologism is but another expression of his general suspicion of cognitive authority of any kind.