Abstract

How many minds do you have? If you are a normal human, I think only one, but a number of dual-process theorists have disagreed. As an explanation of human irrationality, they divide human reasoning into two: Type-1 is fast, associative, and automatic, while Type-2 is slow, rule-based, and effortful. Some go further in arguing that these reasoning processes constitute (or are partly constitutive of) two minds. In this paper, I use the Star Trek ‘Trill’ species to illuminate the condition for the existence of “two minds in one brain” (Evans 2010, 3). After carefully outlining the two dominate versions of dual-process theory (default-interventionism, espoused by Evans, Stanovich, and Kahneman, and parallel-competitive theory, espoused by Sloman, Frankish, and Carruthers) and contrasting each with a one-system alternative, I argue that these three views should be understood as existing on a continuum: there are some theories that could plausibly be characterized as either one-system or default-interventionist, and the distinction between default-interventionism and parallelcompetitive theory is not as clean-cut as usually assumed. I then argue, using the conceptual claims I defended using the science fiction cases, that default-interventionist dual-process theory is not compatible with the claim that humans have two minds (contra Evans and Stanovich).