Abstract

The idea that we acquire knowledge by trial and error has been one of the truly great ideas of the twentieth century. As no reader of his philosophical and autobiographical work could have failed to notice, Karl Popper credits himself for having invented this idea. The theory of trial and error or, in Popper's words, the Searchlight theory of knowledge and mind, is not just a part of Popper's comprehensive philosophy but rather one of its key features. It is at the bottom of some of his most spectacular achievements in methodology, epistemology, the philosophy of biology, and even political philosophy. Indeed, it is put forward at once as a model for the growth of individual knowledge (both human and animal), the growth of life (Darwin's theory of evolution), and the growth of scientific knowledge (philosophy of science). As happens so often with innovative ideas, the Searchlight theory derives much of its glamour from the theory it rejects: the view of the mind being a tabula rasa and sense perception the origin of all (human) knowledge. Popper nicknames this empiricists' view as the Bucket theory since it conceives of the mind as nothing but the conduit for sense-impressions, an empty bucket to be filled by the accumulation and storage of information. 1 In his hands the Bucket theory collapses under the strain of philosophical arguments and scientific facts and is replaced by a theory which maintains that our knowledge of the physical world is drawn from our mind and constructed from the repertoire of knowledge dispositions we already possess. Acquiring dispositions proceeds according to the method of trial and error elimination. This method, Popper contends, consists essentially of three stages: forming a problem or expectation, trying out a number of solutions of the problem, and eliminating or discarding false solutions as erroneous. 2 A key feature of Popper's theory of trial and error elimination, and the reason for speaking of a Searchlight theory of knowledge and mind, is his insistence that problems or expectations take precedence over observations. Observations are always preceded by expectations, points of view, questions or problems which, as a searchlight, illuminate a certain area, thereby enabling the organism or the scientist to know what to observe in the first place. The question arises how and when did Popper come to this theory of the growth of knowledge and mind which was to have such radical implications for the philosophy of science, epistemology, and the philosophy of psychology? My aim in this article is to trace the roots of his theory of the Searchlight. The earliest traces of the theory are to be found in his unpublished dissertation, Zur Methodenfrage der Cognitive psychology (1928). Here I will focus upon this "hasty last minute affair" written in the tradition of early German cognitive psychology and supervised by one of its most outstanding proponents, Karl Bühler. Scrutiny of this manuscript, however, reveals not so much the formative influence of Bühler as that of Otto Selz. Indeed, I will argue that Popper borrowed his crucially important Searchlight theory from Selz. Thus having found the origin of the key notion of his epistemology in psychology, the relation between psychology and philosophy in Popper's work, always fraught with tension, is up for thorough reconsideration.