The vowel inventory of West Frisian is very rich.
- The long vowels are considerably longer than the short vowels. The former are generally over 250 ms, whereas the latter are generally under 150 ms.
- Some speakers merge the long vowels /iː, uː/ with the centering diphthongs /iə̯, uə̯/.
- /yː/ is infrequent. It and the other long close rounded vowel /uː/ are absent from the dialect of Ljouwert.
- Many scholars transcribe /ø/ as /ø/, but de Haan (2010) transcribes it as /ʏ/. Phonetically, it is quite similar to /ə/.
- Although they pattern with monophthongs, the long close-mid vowels transcribed /eː, øː, oː/ are often realized as narrow closing diphthongs [ei̯, øy̑, ou̯]. However, there are exceptions: for instance, speakers of the Hindeloopers dialect realize /øː/ as a long monophthong [øː].
- Nearly all words with /øː/ are loanwords from Standard Dutch.
- /oː/ doesn't occur before /s/.
- Although they pattern with monophthongs, the long open-mid vowels transcribed /ɛː, ɔː/ tend to be realized as centering diphthongs [ɛə̯, ɔə̯].
- The Hindeloopers and Súdwesthoeksk dialects also feature open-mid front rounded vowels /œ, œː/, which are not a part of the standard language.
- Many scholars transcribe /a/ as /a/, but de Haan (2010) transcribes it as /ɑ/. Its phonetic quality has been variously described as central [ä] and back [ɑ].
- /aː/ is central [äː].
- Booij (1989) argues that the rising diphthongs /jɪ, jɛ, wa, wo/ (he also lists the rare /jø/) are in fact glide-vowel sequences, not real diphthongs. This view is supported by Hoekstra & Tiersma (2013) who transcribe them as /jɪ, jɛ, wa, wo/, which is the convention used in this article.
- In Southwestern dialects, /wa, wo/ are monophthongized to short central [ɞ, ɵ].
- The closeness of either of the elements of /ɛi̯/ is somewhat variable, so that its phonetic realization is [æi̯ ~ æɪ̯ ~ ɛi̯ ~ ɛɪ̯].
- The first element of /œy̑/ is more like [œ] than [ø]. Many scholars transcribe this sound as /øy̑/, Booij (1989) transcribes it as /ʌy̑/, yet this article transcribes it /œy̑/ to show that it is clearly distinct from the common diphthongal realization of /øː/ (having a much lower starting point) and that it is virtually identical to /œy̑/ in Standard Dutch.
- Some scholars transcribe /ɔu̯/ as /ɔu̯/, yet others transcribe it as /au̯/. Phonetically, the first element of this diphthong may be either of these, i.e. [ɔ] or, less often, [a].
- Some varieties realize /ai̯/ as [ɔi̯].
- Many speakers round the first element of /aːi̯/ to [ɔː].
Some falling diphthongs alternate with the rising ones:
||'to meander softly'|
- The /yə̯/ - /jø/ alternation occurs only in the pair mentioned above.
- /m, p, b/ are bilabial, whereas /f, v/ are labiodental.
- /v/ has two allophones: an approximant [ʋ], which appears word-initially, and a fricative [v], which occurs elsewhere.
- In some cases, /d/ alternates with /r/.
- /r/ is silent before other alveolar consonants. An exception to this rule are recent loanwords from Standard Dutch (e.g. sport), which may or may not be pronounced with [r].
- /ŋ, k, x, ɣ/ are velar, whereas /j/ is palatal.
- /ɣ/ has two allophones: a plosive [ɡ], which appears word-initially and syllable-initially (the latter only when stressed), and a fricative [ɣ], which occurs elsewhere.
- The syllabic sonorants [m̩, n̩, ŋ̍, l̩, r̩] occur in the following circumstances:
- In the ending ⟨en⟩, which in careful speech is pronounced [ən]:
- It is realized as [m̩] when preceded by /m, p, b/.
- It is realized as [n̩] when preceded by /f, v, n, t, d, s, z, r, l/.
- It is realized as [ŋ̍] when preceded by /k, x, ɣ/.
- In the endings ⟨el⟩ and ⟨er⟩ (in careful speech: [əl] and [ər], respectively), which after consonants are realized as [l̩] and [r̩], respectively.
- In some other cases. See Sipma (1913:36) for more information.
- /j/ and the [ʋ] allophone of /v/ are the only sonorants which cannot be syllabic.
- The sequences /nj, tj, sj, zj/ coalesce to [ɲ, tɕ, ɕ, ʑ].
- Glottal stop [ʔ] may precede word-initial vowels. In careful speech, it may also occur between unstressed and stressed vowel or diphthong.
- Among fricatives, neither /x/ nor any of the voiced fricatives can occur word-initially.
- /l/ is velarized [ɫ] in all environments except before the close front vowels /i, iː, y, yː/, where it is realized as clear [l].
Word-final /b, d/ are realized as voiceless [p, t]. Note, however, that final /b/ is rare, and that in loanwords from Standard Dutch, final /ɣ/ can also appear, and is also devoiced to [x].
- Booij, Geert (1989). "On the representation of diphthongs in Frisian". Journal of Linguistics. 25: 319–332. JSTOR 4176008.
- de Haan, Germen J. (2010). Hoekstra, Jarich; Visser, Willem; Jensma, Goffe, eds. Studies in West Frisian Grammar: Selected Papers by Germen J. de Haan. Amsterdam: John Benjamins Publishing Company. ISBN 978-90-272-5544-0. Retrieved 30 March 2017.
- Hoekstra, Eric (2003). "Frisian. Standardization in progress of a language in decay" (PDF). Germanic Standardizations. Past to Present. 18. Amsterdam: John Benjamins Publishing Company. pp. 193–209. ISBN 978-90-272-1856-8. Archived (PDF) from the original on 30 March 2017. Retrieved 30 March 2017.
- Hoekstra, Jarich (2001). "12. Standard West Frisian". In Munske, Horst Haider; Århammar, Hans. Handbook of Frisian studies. Tübingen: Max Niemeyer Verlag GmbH. pp. 83–98. ISBN 3-484-73048-X. Retrieved 30 March 2017.
- Hoekstra, Jarich; Tiersma, Peter Meijes (2013) [First published 1994]. "16 Frisian". In König, Ekkehard; van der Auwera, Johan. The Germanic Languages. Routledge. pp. 505–531. ISBN 0-415-05768-X. Retrieved 30 March 2017.
- Hof, Jan Jelles (1933). Friesche Dialectgeographie (PDF) (in Dutch). The Hague: Martinus Nijhoff. Archived (PDF) from the original on 7 October 2016. Retrieved 30 March 2017.
- Keil, Benjamin (2003). "Frisian phonology" (PDF). Los Angeles: UCLA Department of Linguistics. Archived (PDF) from the original on 4 March 2016. Retrieved 30 March 2017.
- Sipma, Pieter (1913). Phonology & grammar of modern West Frisian. London: Oxford University Press. Retrieved 30 March 2017.
- Tiersma, Peter Meijes (1999) [First published 1985 in Dordrecht by Foris Publications]. Frisian Reference Grammar (2nd ed.). Leeuwarden: Fryske Akademy. ISBN 90-6171-886-4.
- van der Veen, Klaas F. (2001). "13. West Frisian Dialectology and Dialects". In Munske, Horst Haider; Århammar, Hans. Handbook of Frisian studies. Tübingen: Max Niemeyer Verlag GmbH. pp. 98–116. ISBN 3-484-73048-X. Retrieved 30 March 2017.
- Visser, Willem (1997). The Syllable in Frisian (PDF) (PhD). Leiden: Holland Institute of Generative Linguistics. ISBN 90-5569-030-9. Archived (PDF) from the original on 4 March 2016. Retrieved 30 March 2017.
- Cohen, Antonie; Ebeling, Carl L.; Fokkema, Klaas; van Holk, André G.F. (1978) [First published 1961]. Fonologie van het Nederlands en het Fries: inleiding tot de moderne klankleer (in Dutch) (2nd ed.). The Hague: Martinus Nijhoff.
- Fokkema, Klaas (1961). "Consonantgroepen in de Zuidwesthoek van Friesland". In Heeroma, Klaas Hanzen; Fokkema, Klaas. Structuurgeografie (in Dutch). Amsterdam: Noord-Hollandsche Uitg. Mij. pp. 16–26.
- Heeringa, Wilbert (2005). "Dialect variation in and around Frisia: classification and relationships" (PDF). Us Wurk, tydskrift foar Frisistyk. 3–4: 125–167. Archived from the original (PDF) on 4 March 2016. Retrieved 30 March 2017.
- Tiersma, Peter Meijes (1983). "The nature of phonological representation: evidence from breaking in Frisian". Journal of Linguistics. 10: 59–78. JSTOR 4175665.