Can the Fragmentationist Accept a Formal Account of Irrationality?

ABSTRACT This paper examines a tension between three plausible claims: that violations of formal coherence requirements are paradigmatically irrational; that formal incoherence is best modeled as belief fragmentation; and that fragmentation need not be irrational. I argue that the first claim must be weakened. Some formally incoherent collections of belief are not irrational, because they are not appropriately subject to rational evaluation. Drawing on a Scanlonian notion of judgment‐sensitivity, I propose that only incoherence that is remediable through reasoning constitutes irrationality. This view explains why fragmentation in domains such as perception and motor control is epistemically suboptimal without being irrational, while preserving a role for coherence norms in cases where coordination across fragments is possible.