Where does defeasibility collide?

In law, a claim, right, or interest is defeasible when it holds by default but can be defeated or cut off by further facts: an estate may terminate on a stated condition, or a prima facie right may be overridden by a stronger one. H. L. A. Hart's 1949 The ascription of responsibility and rights drew philosophical attention to this feature of legal concepts, which hold "unless" a defeating condition arises. The referent is the overridable, condition-subject character of legal entitlements.[1]

Unit

Whether an interest or claim holds by default but can be terminated by a defeating condition

Recovery means

Not applicable

Measured by

Identified by the conditions or exceptions that would defeat an otherwise valid claim or interest

In logic and artificial intelligence, defeasible (non-monotonic) inference draws conclusions that may be withdrawn when new premises arrive, unlike classical deduction, where conclusions are permanent. Reiter's A logic for default reasoning formalises default rules that license a conclusion "unless" a recognised exception holds. The referent is a mode of inference whose conclusions are provisional and retractable, sharing the "holds unless defeated" shape with the legal notion but applied to reasoning rather than entitlements.[2]

Unit

Whether a conclusion stands provisionally but can be retracted on new information

Recovery means

Not applicable

Measured by

Formalised through default rules and their extensions, tracking which conclusions survive once exceptions are known

In epistemology, a justification is defeasible when it supports a belief only in the absence of defeaters: further evidence, whether rebutting or undercutting, that would remove the support. Pollock's 1987 Defeasible reasoning develops this account of justified belief and the defeaters that can override it. The referent is the overridable warrant for a belief, distinct from a legal interest or a formal inference rule though built on the same default-and-defeater pattern.[3]

Unit

Whether a belief's justification holds absent defeaters that would undercut or rebut it

Recovery means

Not applicable

Measured by

Analysed through the structure of reasons and defeaters that strengthen or remove justification