Behavioral and Brain Sciences

Continuing Commentary
Commentary on Stanovich, K. E. and West, R. F. “Individual differences in reasoning: Implications for the rationality debate?” BBS 23(5):645–726 [October 2000]

Freud's dual process theory and the place of the a-rational

Linda A. W. Brakel a1 and Howard Shevrin a1
a1 Department of Psychiatry, University of Michigan Medical Center, Ann Arbor, MI 48109-0722


In this commentary on Stanovich & West (S&W) we call attention to two points: (1) Freud's original dual process theory, which antedates others by some seventy-five years, deserves inclusion in any consideration of dual process theories. His concepts of primary and secondary processes (Systems 1 and 2, respectively) anticipate significant aspects of current dual process theories and provide an explanation for many of their characteristics. (2) System 1 is neither rational nor irrational, but instead a-rational. Nevertheless, both the a-rational System 1 and the rational System 2 can each have different roles in enhancing evolutionary fitness. Lastly, System 1 operations are incorrectly deemed “rational” whenever they increase evolutionary fitness.