Abstract
Theories of natural thought processes have traditionally served as foundations for philosophies of science. The source of all knowledge is passively received observations; these are combined to produce certain knowledge. After David Hume showed that this was not possible, deductivist alternatives, that is, theories that find a source of knowledge in ideas not derived from observations, from Immanuel Kant to William Whewell in the mid-19th century, were introduced. In response, traditional associationist and inductivist views were refurbished; a deductivist alternative was developed by the Würzburg School. Much later Karl Popper in philosophy and Donald T. Campbell in psychology integrated this view with evolutionary theory. Campbell wanted thereby to find a justificationist view, which would reduce philosophy of science to cognitive psychology; Popper rejected both justificationism and the reduction of philosophy of science to psychology. Campbell thought all rational processes were innate psychological processes; Popper thought psychological processes were used to develop various rational processes. Campbell could not show that all rational thought was reducible to innate psychological processes, nor how some justification of scientific theories was possible. Popper could not show how evolutionary theory contributed to our knowledge of psychological thought processes. Both failed to observe that cognitive processes are social; people have learned how to think by learning how to interact in social groups seeking understanding. When innate thought processes are studied as social characteristics, evolutionary theory can contribute to both cognitive psychology and the theory of rationality, as both Popper and Campbell wanted it to do.
