A functional theory of semantics that accounts for idioms, rigid expressions, and language variability and indeterminacy is explored. The theory is based on the distinction between language as a natural, social phenomenon and linguistic systems as the constructions of linguists, and avoids the usual tendency of theory to assume that language is a logical system. It allows for explanation of variability as the creation of linguistic forms within given contexts, without attempting to pin it down to a specific rule, and distinguishes between structural and functional indeterminacy. Idioms, metaphors, the use of prepositions with unforseeable illocutions, fantasy, science fiction, and interpretable and uninterpretable nonsense are treated as the result of a form of indeterminacy, or creativity--an unpredictable condition within conventional linguistic theory. (MSE)