Editing Diphthong (section)

===Closing, opening, and centering===
[[File:Belgian Dutch diphthongs chart.svg|thumb|upright=1.15|[[Vowel diagram]] illustrating closing diphthongs of Belgian Standard [[Dutch language|Dutch]], from {{Harvcoltxt|Verhoeven|2005|p=245}}]]
[[File:Orsmaal-Gussenhoven Dutch centering diphthongs chart.svg|thumb|upright=1.15|Vowel diagram illustrating centering diphthongs of the [[Dutch language|Dutch]] dialect of [[Orsmaal-Gussenhoven dialect|Orsmaal-Gussenhoven]], from {{Harvcoltxt|Peters|2010|p=241}}]]
In '''closing''' diphthongs, the second element is more [[close vowel|close]] than the first (e.g. {{IPA|[ai]}}); in '''opening''' diphthongs, the second element is more [[open vowel|open]] (e.g. {{IPA|[ia]}}). Closing diphthongs tend to be falling ({{IPA|[ai̯]}}), and opening diphthongs are generally rising ({{IPA|[i̯a]}}),<ref>{{Cite book|title=Dictionary of Linguistics and Phonetics|editor-last=Crystal|editor-first=David|location=Malden, MA|publisher=Blackwell|year=2008|chapter=diphthong|edition=6|isbn=978-1-4051-5297-6|url={{GBurl|id=6muoEAAAQBAJ|p=146}}|access-date=24 March 2023}}</ref> as open vowels are more [[sonorant|sonorous]] and therefore tend to be more prominent. However, exceptions to this rule are not rare in the world's languages. In [[Finnish phonology|Finnish]], for instance, the opening diphthongs {{IPA|/ie̯/}} and {{IPA|/uo̯/}} are true falling diphthongs, since they begin louder and with higher pitch and fall in prominence during the diphthong.

A third, rare type of diphthong that is neither opening nor closing is '''height-harmonic''' diphthongs, with both elements at the same vowel height.<ref>{{cite book|editor-first1=Richard M.|editor-last1=Hogg|editor-first2=Norman Francis|editor-last2=Blake|editor-link2=Norman Blake (academic)|editor-first3=Robert William|editor-last3=Burchfield|title=The Cambridge History of the English Language|location=Cambridge|publisher=Cambridge University Press|year=1992|volume=1|page=49|isbn=0-521-26475-8|url={{GBurl|id=UlD3ksfXl5IC|p=49}}|access-date=24 March 2023}}</ref> These may have occurred in [[Old English]]:
* ''beorht'' {{IPA|[beo̯rxt]}} "bright"
* ''ċeald'' {{IPA|[t͡ʃæɑ̯ld]}} "cold"

A '''centering''' diphthong is one that begins with a more peripheral vowel and ends with a more central one, such as {{IPA|[ɪə̯]}}, {{IPA|[ɛə̯]}}, and {{IPA|[ʊə̯]}} in [[Received Pronunciation]] or {{IPA|[iə̯]}} and {{IPA|[uə̯]}} in [[Irish language|Irish]]. Many centering diphthongs are also opening diphthongs ({{IPA|[iə̯]}}, {{IPA|[uə̯]}}).

Diphthongs may contrast in how far they open or close. For example, [[Samoan language|Samoan]] contrasts low-to-mid with low-to-high diphthongs:
* '''ai'' {{IPA|[ʔai̯]}} 'probably'
* '''ae'' {{IPA|[ʔae̯]}} 'but'
* '''auro'' {{IPA|[ʔau̯ɾo]}} 'gold'
* ''ao'' {{IPA|[ao̯]}} 'a cloud'