 Pelletier, Asher, and Morreau connect their semantic account of generics to the literature on defeasible validity (McCarthy 1986; Reiter 1987, and others). A set of premises defeasibly or non-monotonically entails a conclusion if the conclusion is likely or reasonable given the premises, yet it is nonetheless possible for the premises to be true and the conclusion false. They argue that there are many defeasibly valid patterns of entailment that involve generics, and that their semantics explains why this is so. For example, if Fido is a dog and dogs have four legs, then the inference that Fido has four legs is held to be defeasibly valid. It is possible that Fido is a three legged dog, but it is still reasonable to suppose that Fido is four legged on the basis of the premises. The reasonableness of this inference is explained on Pelletier, Asher, and Morreau’s semantics—the generic “dogs have four legs” guarantees that, if things go normally for a given dog with respect to its number of legs, then that dog will have four legs. Since we have been given no reason to suppose that Fido is abnormal, one may defeasibly conclude that Fido is four legged.