Aitchison, J. (2013) Language change: progress or decay? 4th ed. Oxford: Cambridge University Press.
Ball, M.J. and Müller, N. (2002) Mutation in Welsh. London: Routledge. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=179983.
Ball, M.J. and Müller, N. (2010) The Celtic languages. 2nd ed. New York, NY: Routledge.
Barber, C.L., Beal, J.C. and Shaw, P.A. (2009) The English language: a historical introduction. 2nd ed. Cambridge: Cambridge University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=431990.
Borsley, R.D., Tallerman, M. and Willis, D.W.E. (2007) The syntax of Welsh. Cambridge: Cambridge University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=321433.
Breitbarth, A. (2010) Continuity and change in grammar. Amsterdam: John Benjamins Pub. Co. Available at: http://bangor.eblib.com/patron/FullRecord.aspx?p=623334.
Campbell, L. (2020) Historical linguistics: an introduction. Edinburgh: Edinburgh University Press.
Campbell, L. and Poser, W.J. (2008) Language classification: history and method. Cambridge, UK: Cambridge University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=352993.
Clackson, J. (2007) Indo-European linguistics: an introduction. Cambridge: Cambridge University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=321426.
Crowley, T. and Bowern, C. (2010) An introduction to historical linguistics. 4th ed. Oxford: Oxford University Press.
Davies, J. (2007) A history of Wales. New rev. ed. London: Penguin.
Davies, P. and Deuchar, M. (2014) ‘Auxiliary deletion in the informal speech of Welsh–English bilinguals: A change in progress’, Lingua, 143, pp. 224–241. Available at: https://doi.org/10.1016/j.lingua.2014.02.007.
Geiriadur Prifysgol Cymru: a dictionary of the Welsh language (1950). Caerdydd: Gwasg Prifysgol Cymru. Available at: https://www.geiriadur.ac.uk/.
Hale, M. (2007) Historical linguistics: theory and method. Malden, MA: Blackwell Pub.
Harbert, W. (2006) The Germanic Languages. Cambridge: Cambridge University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=288493.
Jones, C. (1993) Historical linguistics: problems and perspectives. London: Longman. Available at: https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=697114.
Joseph, B.D. and Janda, R.D. (2003) The handbook of historical linguistics. Malden, MA: Blackwell Pub.
‘Journal of Celtic linguistics’ (1992).
Jucker, A.H. et al. (eds) (2013) Meaning in the history of English: words and texts in context. Amsterdam: John Benjamins Publishing Company. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=1562821.
Konig, E. and van der Auwera, J. (eds) (2002) The Germanic languages. London: Routledge.
Labov, W. (1994) Principles of linguistic change. Oxford, UK: Blackwell.
Lass, R. (1969) APPROACHES TO ENGLISH HISTORICAL LINGUISTICS: AN ANTHOLOGY. HARCOURT COLLEGE.
Lass, R. (1994) Old English: a historical linguistic companion. Cambridge [England]: Cambridge University Press.
Lehmann, W.P. (1992) Historical linguistics: an introduction. 3rd ed. New York: Routledge. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=179291.
MacAulay, D. and Thomas, A.R. (1992) The Celtic languages. Cambridge [England]: Cambridge University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=179053.
Mallory, J.P. and Adams, D.Q. (2006) The Oxford introduction to Proto Indo European and the Proto Indo European world. New York: Oxford University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=430383.
McMahon, A.M.S. (1994) Understanding language change. Cambridge: Cambridge University Press.
Millar, R.M. (2023) Trask’s historical linguistics. Abingdon, England: Routledge. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=7221173.
Mitchell, B. and Robinson, F.C. (1992) A guide to Old English. 5th ed. Oxford: Blackwell. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=819156.
Online Etymological Dictionary (of English) (no date). Available at: https://www.etymonline.com/.
Oxford English Dictionary (no date). Available at: https://www.oed.com.
Ringe, D.A. and Eska, J.F. (2013) Historical linguistics: toward a twenty-first century reintegration. Cambridge [England]: Cambridge University Press. Available at: https://ebookcentral.proquest.com/lib/bangor/detail.action?docID=1099801.
Robinson, O.W. (1992) Old English and its closest relatives: a survey of the earliest Germanic languages. London: Routledge. Available at: https://doi.org/10.4324/9780203393086.
Romaine, S. (1982) Socio-historical linguistics: its status and methodology. Cambridge [Cambridgeshire]: Cambridge University Press.
‘Studia Celtica: bwletin y Bwrdd Gwybodau Celtaidd = the bulletin of the Board of Celtic Studies’ (1994).
Thomason, S.G. (2001) Language contact. Edinburgh: Edinburgh University Press. Available at: https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=80987.
Trask, R.L. (2000) The dictionary of historical and comparative linguistics. Edinburgh: Edinburgh University Press. Available at: https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=2398356.
Treharne, E.M. (2010) Old and Middle English, c.890-c.1450: an anthology. 3rd ed. Chichester, West Sussex: Wiley-Blackwell.
Woodard, R.D. (2004) The Cambridge encyclopedia of the world’s ancient languages. Cambridge: Cambridge University Press.