Logic, Beliefs, and Instruction: A Test of the Default Interventionist Account of Belief Bias Simon J. Handley, Stephen E. Newstead, and Dries Trippas University of Plymouth According to dual-process accounts of thinking, belief-based responses on reasoning tasks are generated as default but can be intervened upon in favor of logical responding, given sufficient time, effort, or cognitive resource. In this article, we present the results of 5 experiments in which participants were instructed to evaluate the conclusions of logical arguments on the basis of either their logical validity or their believability. Contrary to the predictions arising from these accounts, the logical status of the presented conclusion had a greater impact on judgments concerning its believability than did the believability of the conclusion on judgments about whether it followed logically. This finding was observed when instructional set was presented as a between-participants factor (Experiment 1), when instruction was indicated prior to problem presentation by a cue (Experiment 2), and when the cue appeared simultaneously with conclusion presentation (Experiments 3 and 4). The finding also extended to a range of simple and more complex argument forms (Experiment 5). In these latter experiments, belief-based judgments took significantly longer than those made under logical instructions. We discuss the implications of these findings for default interventionist accounts of belief bias. Keywords: reasoning, dual processes, belief bias, instruction, conditionals The idea that human thinking is influenced by the operation of two systems of thought is now a widely accepted position across many subdisciplines of psychology. According to this view, judg- ments are often guided by rapid, unconscious associative pro- cesses, an idea that has been applied in a range of research areas, including learning, memory, reasoning, and social judgment (Evans, 2008). However, it is also recognized that some processes are slow, conscious, and deliberative, drawing on the resources of working memory and executive functions (Evans, 2003). This has led many theorists to argue that responses to reasoning and decision-making tasks arise from the operation of two distinct cognitive systems associated with qualitatively different process- ing characteristics. Type 1 processes (using Evans’s 2009 termi- nology) are rapid, automatic, preconscious, and relatively unde- manding of computational capacity. In contrast, Type 2 processes are controlled, conscious, analytic, and related to individual dif- ferences in working memory capacity and general intelligence. In the reasoning literature, researchers often categorize the re- sponses that their participants generate into these two kinds, var- iously termed analytic or heuristic, deliberative or automatic, ra- tional or intuitive, or rule-based or associative. In such categorizations, a fairly direct correspondence is assumed between a response and its underlying process, such that intuitive responses based upon an apparently superficial problem characteristic are assumed to reflect Type 1 processing, whereas analytic responses based upon the logical structure of an argument are assumed to reflect Type 2 processing. Consider, for example, an argument of the following kind in which there is a conflict between the believ- ability of the conclusion and its underlying logic status (Sa ´, West, & Stanovich, 1999): All plants need water. Roses need water. Therefore, roses are plants. According to dual-process accounts, the intuitive or Type 1 response is to endorse the conclusion because it is consistent with underlying beliefs, whereas the appropriate rejection of the con- clusion is assumed to reflect more deliberative, analytic, or Type 2 processes (Evans, 2009). A key question concerns the way in which these processes interact with one another. A number of proposals in the literature can be broadly categorized as parallel processing or default interventionist accounts (see Evans, 2007b; 2008). Parallel processing models are common in social psychol- ogy (see Chaiken & Trope, 1999) but have also been applied in judgment and decision making through a distinction made by Sloman (1996) between rule-based and associative processes. These models assume that Type 1 and Type 2 processes are initiated in parallel, with Type 2 responses dominating if sufficient resources are available. An alternative and widely held view in the psychology of reasoning proposes that the many demonstrations of biases extant in the literature can be attributed to the dominance of Type 1 processes, which suggest a compelling, if erroneous, re- sponse to a problem before Type 2 processes are fully engaged (Evans, 2007a). In order to generate an alternative response, Type 2 processes must undertake the working memory– demanding task of inhibiting the Type 1 output (see, for example, Handley, Capon, This article was published Online First November 8, 2010. Simon J. Handley, Stephen E. Newstead, and Dries Trippas, School of Psychology, University of Plymouth. Correspondence concerning this article should be addressed to Simon J. Handley, School of Psychology, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, United Kingdom. E-mail: shandley@ plymouth.ac.uk Journal of Experimental Psychology: © 2010 American Psychological Association Learning, Memory, and Cognition 2011, Vol. 37, No. 1, 28 – 43 0278-7393/10/$12.00 DOI: 10.1037/a0021098 28