This article examines idiomatic expressions as sources of both regularity and irregularity in language. Some morphological, lexical, syntactical, and semantical characteristics of idioms are discussed. It is shown how a lexical licensing mechanism, which is formulated within a formal grammar framework, can deal with the data. After that, this proposal is extended to the phenomenon of negative polarity.
KEYWORDS: Irregularity, Regularity, HPSG, Idioms, Bound Words, Polarity Items, German