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. (Contains 1 footnote and 9 tables.)