I've noticed this phenomenon / process in many words where a diphthong (or a long vowel as well?) reduces to a short vowel when it's inflected.

Consider the following examples:

Pronounce /prəˈnns/ → pronunciation /prəˌnʌn.siˈeɪ.ʃən/

Wise /wz/ → wizard /ˈwɪz.əd/

Know /nəʊ/ → knowledge /ˈnɒl.ɪdʒ/

Finite /ˈf.naɪt/ → infinite /ˈɪn.fɪ.nət/

Nature /ˈn.tʃə(r)/ → natural /ˈnætʃ.ər.əl/

In all the above examples, a diphthongs changes to a short vowel when it's inflected.

I searched a lot (shortening/ reduction of vowels to diphthongs etc.) but I did not find any useful information.


  • What is this phenomenon called?
  • Why does this happen?
  • Does it affect all inflected words?

3 Answers 3


There are indeed five diphthongs/long vowels that reduce to a short vowels in some inflections of words. This is a consequence of the Great Vowel Shift: originally, in Middle English, the vowels /aɪ/ and /ɪ/ were simply the long and short versions of the same vowel: /iː/ and /i/ (so crime was pronounced something like we pronounce cream today). The Great Vowel Shift changed all the long vowels substantially, and left the short ones more or less the same.

The five pairs are:

diphthong /aɪ/ to short vowel /ɪ/ (crime, criminal),
diphthong /aʊ/ to short vowel /ʌ/ (foundation, fundamental),
diphthong /eɪ/ to short vowel /æ/ (nation, national),
diphthong /əʊ/ to short vowel /ɒ/ (code, codify),
long vowel /iː/ to short vowel /ɛ/ (brief, brevity).

John Well's Phonetic Blog mentions this in a discussion of why English spelling is so difficult:

Then came major sound changes, notably the Great Vowel Shift, which left us with sets of related words in which the common element is still spelt identically but nowadays pronounced very differently, and in which medieval scribes and printers opted to follow the sense rather than the sound: crime — criminal, type — typical, cave — cavity and so on.

Does this affect all inflected words? No, there are numerous exceptions, like proud, pride, where the vowels are different not because of the Great Vowel Shift, but because they were different in Old English; and scene, scenic, scenery, where the vowel doesn't change with inflections, even though it changes in similar words (zeal, zealot, zealotry). The vowel /iː/ may be conserved in scenic, scenery because the inflected forms date to after the Great Vowel Shift.


As explained in Peter Shor's answer, Middle English had five sets of long and short vowels. Both the long and short vowels had almost the same vowel quality; the difference was only length i.e. the long vowels were simply long.

In certain environments, especially before two or more unstressed syllables, the long vowels became shortened. For example, as Peter Shor said, crime was pronounced /ˈkrm(ə)/ and criminal /ˈkrminəl/: the /iː/ in criminal became /i/ because it was followed by two more syllables. Later on, the Great Vowel Shift changed the vowel qualities of almost all the long vowels, so the /iː/ of crime became /aɪ/.

This process of shortening is called Trisyllabic Laxing and according to Trask's Historical Linguisitcs: ‘At one time, this rule applied to all relevant cases; it was therefore purely a phonological rule, a constraint upon what was pronounceable in English’. Later on, it ceased to be a part of English phonology, however, its remnants can still be found in Modern English:

  • Sincere/sincerity /sɪnˈsɪə/ → sincerity /sɪnˈser.ə.ti/
  • Pronounce/pronunciation /prəˈnns/ → pronunciation /prəˌnʌn.siˈeɪ.ʃən/
  • Derive/derivative /dɪˈrv/ → /dɪˈrɪv.ə.tɪv/
  • Christ/Christmas /krst/ → /ˈkrɪs.məs/
  • Impede/impediment /ɪmˈpd/ → /ɪmˈped.ɪ.mənt/
  • Holy/holiday /ˈhəʊli/ → /ˈhɒlɪdeɪ/

In some cases such as pronounce/pronunciation, announce/annunciation, profound/profundity, it also changed the spelling. The south/southern idiosyncrasy is also because of TSL: southern was a three-syllable word (/ˈsuːðərnə/) when TSL applied, the terminal 'ə' was later on lost and gave us /ˈsʌðən/.

Although there are so many exceptions such as words ending in -ness (mindfulness, loneliness etc) and later borrowings such as obese/obesity [Wikipedia]. In privacy, TSL applies in BrE, but not in AmE, nightingale,

Most of the transcriptions in this answer are from Cambridge Dictionary


The question has already been answered by Peter Shor and Decapitated Soul, but I just wanted to point out that this phenomenon is slightly related to the isochrony of the English language.

See Why are the vowels in Christ and Christmas different? (and other strange diphthong behaviour)

Note that Christ/Christmas or wise/wizard are not examples of Trisyllabic laxing but the phenomenon still happens, which just goes to show that the phenomenon (that, as pointed out by Peter Shor, has its root in the Great Vowel Shift) is more general and related to the isochronic prosody.

  • That is still Trisyllabic Laxing. Jul 6, 2020 at 20:37
  • Christmas and wizard only have two syllables. How can it be trisyllabic anything?
    – Damaru
    Jul 7, 2020 at 7:36
  • 1
    I will explain it in an answer to the question you've linked. Jul 7, 2020 at 8:11
  • Christ vs Christmas - read my answer. Jul 7, 2020 at 21:35
  • 1
    I can't comment there because I don't have 50 of reputation. But great answer, thanks! It makes sense that trisyllabic laxing applied to Christmas at a time in which it actually had 3 syllables. I am not that much convinced about wizard, I have tried to look for old versions of the word and I don't see a 3 syllable version. Then you have the laxing you mention in "tonic". So I still think there is a more general laxing phenomenon beyond the words of three or more syllables.
    – Damaru
    Jul 8, 2020 at 9:28

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