Redundancy rule is rule which fills in predictable or redundant information. Redundancy rules have two important properties: (a) they do not create structure, and (b) they do not alter structure.
the fact that sonorants in English are always voiced, as opposed to obstruents, can be captured by leaving the feature [voice] unspecified, and fill in [+voice] by a redundancy rule. The idea behind redundancy rules and underspecification is that redundant information can be left unspecified in the grammar (usually the lexicon), and that a grammar which contains less (idiosyncratic) information is more highly valued than a grammar which contains more (every thing else being the same).
- Archangeli, D. 1984. Underspecification in Yawelmani Phonology and Morphology, doct. diss, MIT.
- Chomsky, N. and M. Halle 1968. The Sound Pattern of English, Harper and Row, New York.
- Halle, M. 1959. The Sound Pattern of Russian, The Hague, Mouton.
- Kiparsky, P. 1982. From Cyclic Phonology to Lexical Phonology, in: Hulst, H. van der and N. Smith (eds.) The Structure of Phonological Representations (I), pp.131-175
- Stanley 1967. Redundancy Rules in Phonology, Language 43, pp. 393-436