ABSTRACT
The hypothesis that human intelligence does not constitute a unitary system dates back to the origins of psychology. In William James’s manifesto, A Plea for Psychology as a “Natural Science”, published in 1892, James argues that the foundation of psychology as a natural science is based on an intertwining between the notion of adaptation and the notion concerning the levels of consciousness. This functionalist concept – for which the content of thought flow (another concept coined by James) comes into awareness only when “there is need for it” – is taken up again in a recent book and article by Jonathan Evans (2007a, 2007b). Evans develops this intuition by breaking it down into specific hypotheses, and appeals to it for interpreting many experimental data in the field of judgement, reasoning, and decision making. This chapter is dedicated to the two systems of human intelligence in Evans’s model.
