Here I introduce Graham Wallas who applied the study of instincts to the science of politics. Unlike many previous glosses of the rise of mass psychology as the eclipse of reason, careful reading and situation of Wallas’ within the developing field of the social sciences in Britain demonstrate that the application of human nature and biological instincts to the study of politics was an avowed attempt to render the inquiry more scientific. Here the discussion of instincts, an important element of the model Simon calls the ‘Cambridge Mind’, was not a species of anti-democratic thinking or illustrative of the ‘eclipse of reason’ in thought and philosophy, but a revision of the hedonic calculus of Bentham and others. I also discuss William James in all of this in order to underscore that the Cambridge Mind drew from a wide variety of sources, not merely in the UK.