In search of counter-examples: Deductive rationality in human reasoning Walter Schroyens and Walter Schaeken University of Leuven, Leuven, Belgium Simon Handley University of Plymouth, Plymouth, UK Dual-process theories come in many forms. They draw on the distinction between associative, heuristic, tacit, intuitive, or implicit processes (System 1) and rule-based, analytic, explicit processes (System 2). We present the results of contextual manipulations that have a bearing on the supposed primacy of System 1 (Stanovich & West, 2000). Experiment 1 showed that people who evaluated logically valid or invalid conditional inferences under a timing constraint (N = 56), showed a smaller effect of logical validity than did people who were not placed under a timing constraint (N = 44). Experiment 2 similarly showed that stressing the logical constraint that only inferences that follow necessarily are to be endorsed (N = 36) increased the size of the validity effect, as compared to that of participants (N = 33) given the standard instruction to make “logi- cal” inferences. These findings concur with the thesis in dual-processing frameworks that “Rationality-2 processes” (Evans & Over, 1996), “test procedures” (Chater & Oaksford, 1999), or “conclusion validation processes” (Johnson-Laird & Byrne, 1991; Schroyens, Schaeken, & d’Ydewalle, 2001) serve to override the results of System 1 processes. Presently there is a growing consensus about the thesis that a distinction can be made between two types of rationality, or systems of reasoning (see, e.g., Evans & Over, 1996, 1997; Johnson- Laird, 1983; Sloman, 1996; Stanovich, 1999; Stanovich & West, 2000). Dual-process theories of reasoning draw on the distinction between, on the one hand, highly contextually dependent, associative, heuristic, tacit, intuitive, or implicit processes, which are holistic, automatic, experiential in nature and relatively undemanding of cognitive capacity and, on the other hand, contextually independent, rule-based, analytic, explicit processes, which are relatively slow and demanding of cognitive capacity. As regards the functional relation between the two Requests for reprints should be sent to Walter Schroyens, University of Leuven, Department of Psychology, Laboratory of Experimental Psychology, Tiensestraat 102, B-3000 Leuven, Belgium. Email: Walter.Schaeken@psy.kuleuven.ac.be Both W. Schroyens and W. Schaeken are supported in their research as senior research fellows of the Flanders Fund for Scientific Research (Belgium, FWO). Reporting this work was in part funded by a foreign travel grant of the FWO awarded to W. Schroyens, for a stay at the University of Plymouth (UK). We would like to thank Mike Oaksford and two anonymous reviewers for their comments on preview drafts of the manuscript.  2003 The Experimental Psychology Society http://www.tandf.co.uk/journals/pp/02724987.html DOI:10.1080/02724980245000043 THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2003, 56A (7), 1129–1145