Belief Bias

Belief bias is the tendency to judge the logical strength of an argument based on the believability of its conclusion rather than on whether the argument's structure actually follows valid logical rules, so that a valid argument leading to an implausible conclusion is often judged invalid, while an invalid argument leading to a believable conclusion is often judged valid. The effect has been studied in the psychology of reasoning since foundational work in the 1980s by researchers including Jonathan Evans and colleagues, who used syllogistic reasoning tasks that systematically crossed logical validity with the believability of the conclusion to isolate the two influences on participants' judgments. Belief bias is discussed as key evidence for dual-process theories of reasoning, in which a fast, intuitive judgment based on plausibility competes with a slower, more effortful process of genuine logical evaluation, with the intuitive route often winning when the two conflict.