Crystal, D. (2008). A Dictionary of Linguistics and Phonetics. 6th Edition, Blackwell Publishing.
Ellis, R. (1994). The study of second language acquisition. Oxford: Oxford University Press.
Gussenhoven, C., & H. Jacobs (2011). Understanding Phonology. Great Britain: Hodder Education.
Richards, J. C., & R. Schmidt (2002). Longman Dictionary of Language Teaching and Applied Linguistics. 3rd Edition, Pearson Education Limited.