↑ Brinton, Laurel J. (2000). The Structure of Modern English: A Linguistic Introduction. Amsterdam, Philadelphia: John Benjamins. tr. 104. ISBN9781556196621.
↑ Anderson, Stephen R. (1985), “Inflectional Morphology”, trong Shopen, Timothy, Language typology and syntactic description, Cambridge, New York: Cambridge University Press, tr. 162–164
