Delusions, Evidence, and the Limits of Epistemic Classification

The orthodox view in both clinical and philosophical literature is that delusions are fixed beliefs that resist revision despite contrary evidence. The assumption that delusions are fixed is central to diagnostic criteria and theoretical accounts of delusions and has influenced broader discussions about their rationality and epistemic status. In this paper, I argue that the orthodox view is misleading; delusions are not fixed in a distinctive sense that clearly defines their characteristics or permits straightforward classification within psychiatric systems. Empirical and clinical research show that many delusions respond to evidence over time, and a comparative analysis reveals that some entrenched non-delusional beliefs can be just as resistant, or even more resistant, to revision. No standard of evidence-responsiveness I consider justifies labeling delusions as epistemically unique because of their resistance to evidence. Consequently, describing delusions as uniquely fixed beliefs is unproductive for explanation or diagnosis, which has important implications for psychiatric taxonomy and our understanding of delusions and how to treat them effectively.