Baker, Ann.1981. Ship or Sheep?: An Intermediate Pronunciation Course. 2nd ed. Cambridge, UK: Cambridge University Press.
2.
Bauer, Laurie.1990. Level Disorder: The Case of -er and -or. Transactions of the Philological Society88:97—110.
3.
———. 1995. Another Marginal Phoneme of English. In Proceedings of the XIIIth International Congress of Phonetic Sciences , edited by Kjell Elnius and Peter Branderud, 3:354-357. Stockholm : KTH and Stockholm University.
4.
Chomsky, Noam.1964. Current Issues in Linguistic Theory. The Hague; Paris: Mouton.
5.
Dinnesen, Daniel.1985. A Re-examination of Phonological Neutralization. Journal of Linguistics21:265—79.
6.
Kelly, John, and John Local.1989. Doing Phonology. Manchester: Manchester University Press.
7.
Lass, Roger.1984. Phonology. Cambridge: Cambridge University Press.
8.
Robinson, Orrin W.2000. Whose German?: The ach/ich Alternation and Related Phenomena in Standard and Colloquial. Amsterdam; Philadelphia, PA: Benjamins.
9.
Saussure, Ferdinand de.1916. Cours de Linguistique Générale. Paris : Payot.
10.
Wells, J.C.1982. Accents of English. 3 vols. Cambridge: Cambridge University Press .