Generics are statements such as ‘dogs are mammals’, ‘a tiger is striped’, ‘the dodo is extinct’, ‘ducks lay eggs’ and ‘mosquitoes carry the West Nile virus’. Generic statements express general claims about kinds, rather than claims about particular individuals. Unlike other general statements such as ‘all dogs are mammals’ or ‘most tigers are striped’, generics do not involve the use of explicit quantifiers (such as ‘all’ or ‘most’ in these examples). In English, generics can be expressed using a variety of syntactic forms: bare plurals (e.g. ‘ducks lay eggs’), indefinite singulars (e.g. ‘a tiger is striped’) and definite singulars (‘the dog is a mammal’). (Sometimes, habitual statements such as ‘Mary smokes’ or ‘John runs in the park’ are classified as generics, but we will not follow this practice here.)
The truth conditions of generics have proved quite puzzling for theorists. For example, ‘dogs are mammals’ seems to require for its truth that all (possible) dogs be mammals. ‘A tiger is striped’ or ‘ravens are black’, however, are somewhat more forgiving, since they are compatible with the existence of a few stripeless albino tigers, and white albino ravens. ‘Ducks lay eggs’ and ‘a lion has a mane’ are more forgiving still; these generics are true even though it is only the mature members of one gender which possess the relevant properties. This truth-conditional laxity is limited in scope, however: we do not accept ‘ducks are female’ or ‘lions are male’, even though every egg-laying duck is a female duck, and similarly mutatis mutandis for maned lions. Finally, we accept ‘mosquitoes carry the West Nile virus’, even though fewer than 1 per cent of mosquitoes carry the virus, while also rejecting ‘books are paperbacks’, when over 80 per cent of books are paperbacks. The correct analysis of the truth conditions for generics is a matter of great controversy among theorists working on the problem.
Number-neutral bare plurals and the multiplicity implicature
