Defeasible Reasoning - Specificity

Specificity

One of the main disputes among those who produce systems of defeasible reasoning is the status of a rule of specificity. In its simplest form, it is the same rule as subclass inheritance preempting class inheritance:

(R1) if p then (defeasibly) q e.g., if penguin then not-flies (R2) if r then (defeasibly) not-q e.g., if bird then flies (O1) if p then (deductively) r e.g., if penguin then bird (M1) arguably, p e.g., arguably, penguin (M2) R1 is a more specific reason than R2 e.g., R1 is better than R2 (M3) therefore, arguably, q e.g., therefore, arguably, not-flies

Approximately half of the systems of defeasible reasoning discussed today adopt a rule of specificity, while half expect that such preference rules be written explicitly by whoever provides the defeasible reasons. For example, Rescher's dialectical system uses specificity, as do early systems of multiple inheritance (e.g., David Touretzky) and the early argument systems of Donald Nute and of Guillermo Simari and Ronald Loui. Defeasible reasoning accounts of precedent (stare decisis and case-based reasoning) also make use of specificity (e.g., Joseph Raz and the work of Kevin D. Ashley and Edwina Rissland). Meanwhile, the argument systems of Henry Prakken and Giovanni Sartor, of Bart Verheij and Jaap Hage, and the system of Phan Minh Dung do not adopt such a rule.