Ability Modals and Distribution over Disjunction

Studies in Logic, Vol. 14, No. 3 (2021): 70–81  PII: 1674-3202(2021)-03-0070-12

Chaoan He

Abstract.

In standard modal logics, existential modals, such as possibility or permission, generally distribute over disjunction. Ability modals, employed to state what an agent can do, as illustrated by Kenny’s classical examples, seem to resist Distribution over Disjunction in certain cases. That is usually taken to indicate that ability modals are not really existential modals. I argue that some sort of success rate is usually implicitly referred to in ability statements, and the concealing of such success rates gives rise to a scope ambiguity. Making explicit such ambiguities will demonstrate that cases such as Kenny’s fail to show that ability modals may resist Distribution over Disjunction. Ability modals, like typical modals associated with locutions such as ‘could’, ‘may’ and ‘might’, may continue to assume their logico-semantic status as existential quantifiers, and there is no need, as far as these cases are concerned, to develop separate logics for abilities.