Reasons for Action and Defeasibility*

This chapter analyzes the question of whether reasons for action are, or can be considered, defeasible. It distinguishes between two different kinds of defeasibility — epistemic and ontological — and applies these two concepts to reasons for action. Based on a realist understanding, the idea of a defeasible reason is simply nonsense: for if reasons are facts in the realist sense they cannot be defeasible. A statement in which defeasibility is predicated of a reason would thus be a self-contradictory statement. This is why, according to such a view, sentences such as ‘φ is a prima facie (defeasible) reason for doing what has been φ-ed’ must necessarily be interpreted by alluding to an epistemic problem, if we want to avoid contradictions within a realistic stance. Following an alternative, ‘constructivist’ understanding, defeasibility may instead be regarded not only as a predicate of reasons, but also as an inescapable property of them, since the existence of a reason for a specific action depends on a set of human beliefs and attitudes: this in turn makes it possible to assert without contradiction that something is a reason and is defeasible in itself.