Penultimate Draft Psychologism, History of M. Kusch University of Vienna, Austria The history of psychologism is the history of an accusation and of a threat. To label authors as advocates of psychologism is to claim that they use psychological concepts and ideas in the wrong place. The accusation first became popular in the German-speaking world with the rise of experimental psychology in the second half of the nineteenth century. The most famous episode in the history of the accusation is the 'psychologism controversy' in the German-speaking world at the beginning of the twentieth century. Frege and Husserl were among the leading critics of psychologism in logic, mathematics, and epistemology. The German debate over psychologism influenced subsequent philosophical thinking in most Western countries. The history of psychologism is the history of an accusation and of a threat. To label an author an advocate of psychologism is to claim that he or she uses psychological concepts and ideas in the wrong place. The accusation first became popular in the German-speaking world with the rise of experimental psychology in the second half of the nineteenth century. The most famous episode in the history of the accusation is the German 'psychologism controversy' at the beginning of the twentieth century. It will be the central topic of this article. It is widely accepted that this controversy played an important role in shaping the character of Western philosophy in general and analytic philosophy in particular. It also influenced subsequent debates over 'sociologism.' 1 The Psychologism Controversy in Early Twentieth-century Germany From the 1880s onwards, a number of German logicians and epistemologists started to attack some of their philosophical colleagues for presenting and endorsing the following kinds of 'psychologistic' arguments: Logic studies specific 'laws of thought.' Psychology is the study of all kinds of laws of thought. Therefore, logic is a part of psychology. Normative disciplines must be based upon descriptive-explanatory disciplines. Logic is a normative discipline with respect to human thinking. Psychology is the descriptiveexplanatory discipline with respect to human thinking. Therefore, logic must be based upon psychology. Logic is concerned with judgments, concepts, and inferences. Judgements, concepts, and inferences are human mental entities. Therefore, logic is a theory about human mental entities. The touchstone of logical truth is self-evidence. Self-evidence is a human mental experience. Therefore, logic is about a human mental experience (and thus a part of psychology). We cannot conceive of a radically different logic. The limits of conceivability are our mental limits. Therefore, logic is relative to the human species, and thus a subfield of human psychology. In some cases there was considerable dispute concerning the question who actually held these views. The first argument can be found in Theodor Lipps and Gerardus Heymans, the second in Wilhelm Wundt, the third in Wilhelm Jerusalem and Christoph Sigwart, the fourth in Theodor Elsenhans, and the fifth in Benno Erdmann. All the accused had published widely on psychological issues, and some of them openly advocated treating psychology as the foundation of philosophy. Arguments against these and other allegedly psychologistic authors were provided by many writers, amongst them the logician and mathematician Gottlob Frege, the phenomenologist Edmund Husserl, and the Neokantians Hermann Cohen, Paul Natorp, Heinrich Rickert, and Wilhelm Windelband. Of these and the many other critics, Husserl was undoubtedly the most successful. Husserl's arguments appeared in the Prolegomena to his Logische Untersuchungen. The following arguments figured centrally in the debate: If logical rules were based upon psychological laws, then all logical rules would have to be as vague as the underlying psychological laws. But, not all logical rules are vague. Therefore, not all logical rules are based upon psychological laws. If laws of logic were psychological laws, then they could not be known a priori. They would be more or less probable rather than certain, and justified only by reference to experience. But, laws of logic are known a priori; they are justified by apodictic selfevidence, and certain rather than probable. And therefore, laws of logic are not psychological. If logical laws were psychological laws, they would refer to psychological entities. But, logical laws do not refer to psychological entities. And therefore, logical laws are not psychological laws. All forms of psychologism imply relativism. Psychologistic thinkers take logic to be true only for the human species. But this contradicts the meaning of truth. Truths are unchanging, and independent of the human mind. A good deal of the psychologism controversy concerned the validity and originality of Husserl's arguments. Several commentators maintained that Husserl's first three arguments all begged the question. Others challenged Husserl's claim that the laws of logic did not imply matters of fact. Husserl's critics also denied that truths were eternal or independent of human thought. The debate over psychologism was vigorous. This can be seen, for instance, from the fact that more than 130 philosophers were accused of advocating psychologism and that there were as many symptoms and definitions of psychologism as there were philosophical schools (Kusch 1995). It was not merely the relationship between logic and psychology that was at issue, but the relationship between psychology and philosophy as a whole. This was a pressing issue not least because the practitioners of the then new (experimental) psychology worked in philosophy departments, and because between 1873 and 1913 the number of full professorships held by these 'psychologists' increased from one to ten. Of the 39 full professorships in philosophy in 1892, practitioners of experimental psychology held three; of the 42 full professorships in 1900 they occupied six; while of the 44 full professorships in 1913 they had already gained 10. Practitioners and advocates of the new psychology sometimes claimed that psychology provided the key to real progress in philosophy or that it was the heart of philosophy (Ash 1995, Kusch 1995, 1999). This last-mentioned contention was opposed by a quickly growing group of 'pure' philosophers-led by the Neokantians, and by Eucken, Dilthey, and Husserl. They deemed it harmful to philosophy and its progress that experimental psychology should be regarded as part and parcel of philosophy. To put it another way, these philosophers believed that the role of the philosopher, as suggested by the academic success of experimental psychology, needed purification. The prolonged debate between the advocates and opponents of psychology as a philosophical discipline was eventually brought to an end by World War I. The war brought about an atmosphere in which attacks on one's colleagues were regarded as utterly inappropriate. Moreover, it also led to a clear division of labor between pure philosophers and psychologists: while pure philosophy concentrated on the ideological task of celebrating the German 'genius of war,' experimental psychology focused on the training and testing of soldiers. After the war, both academic pure philosophy and experimental psychology had to cope with, and accommodate to, an intellectual environment that was hostile to science, rationality, and systematic knowledge. The project of a scientifically minded philosophy with experimental psychology as its central pillar quickly lost support. Advocates and practitioners of experimental psychology therefore had to find new ways of justifying their work. Many of them continued their wartime involvement with applied psychology (Kusch 1995). 2 The Influence of the Psychologism Controversy 2.1 Psychologism and Sociologism The way the psychologism controversy was fought by the defenders of philosophical purity became an important model for subsequent disputes between advocates and opponents of 'naturalism' (the view that philosophical questions can be answered using the results of the natural and social sciences). Many later arguments against 'sociologism' or 'biologism' closely mirror Frege's and Husserl's ideas. For instance, in the German-speaking world the psychologism controversy of the first two decades of the twentieth century was followed by the dispute over the nature and philosophical aspirations of the sociology of knowledge. Accusations of 'sociologism' surfaced quickly and 'sociologism' was seen by many as the 'successor' to psychologism. Again many philosophers felt that a special science-this time sociology-was trying to occupy philosophical terrain. Critics of the sociology of knowledge accused it of both psychologism and sociologism, and in so doing, they drew on Husserl's work in particular. Defenders of the sociology of knowledge tried a similar feat in presenting their work as a bulwark against psychologism (Meja and Stehr 1990). This idea has become a general feature of the field to this day (Bloor 1983). The close link between the two 'isms' has been transmitted to subsequent Anglophone thinking mainly through the work of Sir Karl Popper. 2.2 Psychologism and Philosophy German-speaking philosophy of the turn of the century exerted a powerful and lasting influence on philosophy in many other countries. Frege's and Husserl's (1970) antipsychologism thus became the dominant view in Western philosophy for much of the twentieth century. This is not to deny that other countries also had their own debates over the relation between psychology and philosophy. In the UK, for instance, George Frederick Stout and James Ward emphasized the philosophical significance of psychology; British Idealists like Francis Herbert Bradley and Brand Blanshard were sympathetic to psychology even though they denied its philosophical credentials; and realists like John Cook Wilson, Bertrand Russell, Herbert Joseph, and Herbert Prichard insisted on a separation. For Prichard, psychology was not even a 'proper science' (Passmore 1994). The institutional separation of psychology from philosophy eventually removed one important source of conflict. Once institutional separation had been achieved, 'pure' philosophers and 'impure' philosophers (i.e., psychologists) were no longer in direct competition over academic chairs. On the plane of ideas, however, the psychological challenge has remained. Throughout the twentieth century, psychology exerted a powerful pull on philosophers who wished to put philosophy on the sure path of a natural science. Willard Van Orman Quine explicitly called for a return to psychologism in the 1960s. Such calls have kept the psychologism accusation alive. Amongst the accused one can find the names of Rudolf Carnap, Michael Dummett, Peter Geach, Nelson Goodman, Thomas Kuhn, John McDowell, Karl Popper, Wifrid Sellars, and Ludwig Wittgenstein. It is now common amongst historians of philosophy and psychology to lament the outcome of the psychologism controversy. The separation of philosophy from psychology delayed the development of research programs like 'cognitive science' that combine psychological experimentation with philosophical aspiration. 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