Why Should We Be Realists About Beliefs? The Rational Indispensability Argument for Realism

Abstract

This paper defends realism about beliefs by presenting the rational indispensability argument, which claims that beliefs are indispensable for explaining how norms of rationality shape human behaviour. I begin by examining the normative aspect of belief ascription and the essential connection between beliefs and rationality highlighted in logic and cognitive psychology. Mild anti-realism, as articulated by Posłajko, allows beliefs to exist for explanatory purposes but denies them natural properties, claiming they are not causally efficacious or strictly individuatable. Against this, I argue ? drawing on Wundt?s argument about the relationship between normative disciplines and descriptive sciences ? that if rationality norms influence human reasoning, then beliefs must be real in a robust, naturalistic sense: causally efficacious and individuatable. I adapt the Quine-Putnam indispensability argument from the philosophy of mathematics to argue that our best theories of rationality require ontological commitment to beliefs as real entities. I conclude, contra Posłajko, that recognising the explanatory role of rationality norms commits us to a realist metaphysics of belief.