Rule feature is a type of diacritic feature which triggers (or blocks) the application of a phonological rule. This feature is usually assumed to account for irregular word formation.
Alternations such as foot:feet, goose:geese and tooth:teeth can be accounted for by assuming that the words foot, goose and tooth, have a rule feature [+U] which triggers the phonological umlaut rule.
- Chomsky, N. and M. Halle 1968. The Sound Pattern of English, Harper and Row, New York.
- Kenstowicz, M. and C. Kisseberth 1979. Generative Phonology: Description and Theory, New York: Academic Press.
- Zonneveld, W. 1978. A Formal Theory of Exceptions in Phonology, Peter de Ridder Press, Lisse.