Describes any one of a number of deductive systems developed to provide a formal account of a sentence’s being meaningless or nonsensical. In philosophy, a number of theories of language have proposed that some apparently grammatical sentences are meaningless, e.g., a sentence being an unverifiable value judgement (‘The Madonna of the Long Neck is a beautiful painting.’), a category mistake (‘Julius Caesar is divisible by two.’), or paradoxical (‘The set of all sets is a member of itself.’). The latter example—in the form of Russell’s Paradox—motivated the independent development of logics of nonsense by logicians Sören Halldén and Dmitri Bochvar.