When Words Speak Louder than Actions: Delusion, Belief, and the Power of Assertion

Rose, D., Buckwalter, W., & Turri, J. (2014). When words speak louder than actions: delusion, belief and the power of assertion. Australasian Journal of Philosophy, 92(4), 683–700.

People suffering from severe monothematic delusions, such as Capgras, Fregoli or Cotard patients, regularly assert extraordinary and unlikely things. For example, some say that their loved ones have been replaced by impostors. A popular view in philosophy and cognitive science is that such monothematic delusions aren’t beliefs because they don’t guide behavior and affect in the way that beliefs do. Or, if they are beliefs, they are somehow anomalous, atypical, or marginal beliefs. We present evidence from five studies that folk psychology unambiguously views monothematic delusions as stereotypical beliefs. This calls into question widespread assumptions in the professional literature about belief’s stereotypical functional profile. We also show that folk psychology views delusional patients as holding contradictory beliefs. And we also show that frequent assertion is a powerful cue to belief-ascription, more powerful than even a robust and consistent track record of non-verbal behavior.