Monotonic logic

Monotonic logic is a logical system in which the set of entailed conclusions only grows as the set of premises expands — conclusions, once derived, are never retracted. If a set of premises Γ entails a conclusion φ, then any superset of Γ also entails φ. The monotonicity property guarantees that learning new information can only add to what is known; it can never invalidate previous inferences.

Classical logic — propositional and first-order — is monotonic. This is a feature and a limitation. It is a feature because it guarantees the stability of inference: a proof, once valid, remains valid. It is a limitation because most real reasoning is non-monotonic: a default assumption (birds