41. Unexpected Vowels in Derived Words


Words of similar spelling but different grammatical class mostly have the same vowel sound(s) and letter(s), but there are numerous exceptions


Some years ago, I was privileged to teach English in South Sudan. It was common to hear the students from the area refer to themselves as “Southerners” (North and South Sudan at the time being a single huge country). However, the way they pronounced this word differed from what I as an Englishman expected it to be.

In my way of speaking, words derived from south (southern, southerner, southerly – see 151. Ways of Using Compass Words) are pronounced with a different first vowel sound: not like that of mouth, but rather /ʌ/, as at the start of suffer (this illogical pronunciation is one of those listed in my earlier pronunciation post, 29. Illogical Vowel Spellings). The people of South Sudan, however, generally kept the vowel unchanged.

Like many departures from standard English, the South Sudanese pronunciation seems more logical, since it follows the more normal English practice of not changing vowels in derived words. Any number of examples of unchanged vowel use can be found, such as the following (the syllables in question being underlined):








Ever since that time in the Sudan, I have wondered how often it happens that a vowel in an English word is pronounced and/or spelt differently from the corresponding vowel in another word based on the same root. Here I present the differences of spelling and/or pronunciation that I have so far managed to observe. 

Note that I am talking about changes of both pronunciation and spelling. Sometimes a vowel is spelt the same in two related words but pronounced differently, as in south and southerner. On other occasions, the two spellings are different too, for example in destroy and destruction. In yet more cases, there are different spellings but no pronunciation change, as in proceed and procedure.

Before proceeding to the word lists, though, I need to exclude a type of vowel pronunciation change that most observers would consider to be regular in English.



It is quite common for a vowel in a root word to become either /ə/ or /ɪ/ in a word derived from that root. Take the first and last vowels of photograph: /əʊ/ and /ɑ:/. These both change into /ə/ in photography. The reason is the influence of word stress, which is the special strength that one syllable in nearly every English word is pronounced with (see 91. Pronunciation in Reading Aloud and 125. Stress and Emphasis). It is normally the case that a stressed syllable is pronounced with the expected vowel pronunciation, while an unstressed syllable must be said with the vowel changed to /ə/ or /ɪ/. The pho- of PHOtograph is stressed and so the vowel pronunciation matches the letter, but that of phoTOgraphy is unstressed, and so its vowel becomes /ə/. 

It can also happen that /ə/ in a root word will change into the more expected pronunciation of its letter in a word derived from that root. Take the middle vowel in INdustry, which should be pronounced /ə/ because the stress is on in-. In the derived adjective inDUStrial, the stress moves onto -dus-, and the vowel becomes /ʌ/. To take one more example, consider the verb and noun uses of reject. The verb stresses -ject, so that unstressed re- is pronounced /rɪ-/, while the noun stresses re-, changing its pronunciation into /ri:-/ (see 86. The Pronunciation of “e” and “i”).

Most of these normal stress-related vowel changes are not the focus of this post. The exception is where the spelling is changed in the derived word as well as the pronunciation. In the examples just presented, the vowels in question did not change their spelling. An example of changed spelling when a vowel becomes /ə/ is repetition derived from repeat. 



The aim of this section is just to present a list of unpredictable vowel changes in order to assist those learners of English who might benefit from having such lists. The changes are classified according to the vowels involved.


1. Spelling Changes Accompanying a Pronunciation Change to /ə/ or /ɪ/


repeat – repetition

maintain – maintenance

abstain – abstinence  (also sustain)

explain – explanation

proclaim – proclamation (also exclaim, reclaim, acclaim, declaim)


2. Spelling Changes with no Pronunciation Change


proceed – procedure

float – flotation

fire – fiery

deny –denial

rely – reliant (also defy)

happy – happiness (also ready, heavy, hearty, dizzy, sturdy)

vigour – vigorous (also rigour, rancour, humour, vapour)

honour – honorable (also favour)


3. Pronunciation Change from /aɪ/ to /ɪ/

This change is not always exceptional (a change to /ɪ/ is quite common when a vowel becomes unstressed), but “regular” changes are worth including because so many are problematic for learners of English:



crisis –critical

wise – wisdom

crime – criminal

wild – wilderness

title – titular

bible – biblical

emphasise – emphasis (also hypothesise)

incline – inclination (also combine)

revise – revision (also excise, precise)

decide – decision (also deride, elide)

recognise – recognition

ignite – ignition

unite – unit/unity/unify

futile − futility

cycle – cyclic



prophesise – prophecy

summarise – summary (also harmonise)

imply – implication (also multiply)

unify – unification (also magnify, clarify, purify and most other –fy verbs)


4. Pronunciation Change to /ʌ/



south – southern(er)/southerly

occur – occurrence (also recur, concur)



abound – abundance

pronounce – pronunciation (also announce, denounce, enounce)

destroy – destruction

introduce – introduction (also deduce, reduce, induce, seduce, produce)

assume – assumption (also presume, resume, consume)


5. Pronunciation Change to /e/



demolish demolition

prepare – preparation

revere – reverence

heal – health (also steal)

breathe – breath

clean – cleanliness

diabetes – diabetic



retain – retention (also detain, abstain)

example – exemplify

sale – sell

long – length (also strong)

broad – breadth

cease – cessation

intercede – intercession (also recede, concede, accede)

proceed – procession

exceed – excess (also succeed)

receive – reception (also deceive, conceive, perceive)

redeem – redemption


6. Other Changes


doctrine – doctrinal (/ɪ/ to //– also urine, intestine)

adjective – adjectival (/ɪ/ to /aɪ/)

satisfy – satisfaction (// to /æ/ – also putrefy)

clear – clarify (/ɪə/ to /æ/)

compare – comparison (// to /æ/)

mania − manic (/eɪ/ to /æ/)

nation − national (/eɪ/ to /æ/)

feed – food (/i:/ to /u:/ (also teethe)

diminish – diminution (/ɪ/ to /ju:/)

suspect – suspicion (/e/ to /ɪ/)

appropriate (adj) – appropriate (verb) (/ə/ to //, both unstressed – also approximate)

estimate (noun) – estimate (verb) (/ə/ to //, both unstressed)

sell – sale (/e/ to //)

choose – choice (/u:/ to /ɔɪ/)

lose – loss (/u:/ to /ɒ/)

heat – hot (/i:/ to /ɒ/)

diagnose – diagnostic (/əʊ/ to /ɒ/)

microscope – microscopic (/əʊ/ to /ɒ/)

episode – episodic (/əʊ/ to /ɒ/)


I am certain that these lists are incomplete, and I will add to them as and when I can. Meanwhile, readers are also invited to offer suggestions via the comment facility below.


3 thoughts on “41. Unexpected Vowels in Derived Words

  1. Hi, just wanted to point out that these vowel changes are quite predictable, and that many of them occurred by a process called “trisyllabic laxing”, where (Middle English) vowels were shortened if two syllables followed, especially in Classical Compounds from Latin and Greek. As for “south, southerner” and “pronounce, pronunciation”, you have to know that the Modern English /aʊ/ derives from an earlier Middle English “long u” /u:/ sound, which was shortened to /ʌ/.
    The example of food vs feed and tooth vs teeth (also goose vs geese and mouse vs mice and louse vs lice) is due to an entirely different sound change that happened at a much earlier stage in the language. It is due to a common phenomenon in Germanic Languages called “I-mutation” or “I-umlaut”. This would cause a back vowel to become fronted (and possibly unrounded) if the following syllable contained the front vowel sound /i/ or the “Y-sound” /j/. The suffix which caused the vowel changes in these words is now lost. For example, the Proto-English plural form of “tooth” would be something like *toth-iz. The vowel in the first syllable was fronted, possibly going through a front-rounded intermediate vowel before unrounding, and the suffix that caused the change was lost. The overall progression of the change was something like (*o > *ø? (German ö sound, unattested in spelling) > *e) The /o/ and /e/ vowel sounds were raised to /u/ and /i/ during the Great Vowel Shift. Words like “mouse” and “louse” where spelled as “mus” and “lus” /mus/ and /lus/ in Old English. The plurals were something like “mus-iz” and “lus-iz”, so the /u/ vowel was fronted, possibly first to the German ü vowel (transcribed as /y/ in IPA), and was eventually changed to /i/. (*u > *y > *i). Both the /i/ and /u/ vowels diphthongized to /ai/ and /au/ during the the Great Vowel Shift. The “I-mutation” process also sporadically fronted the vowel /a/, changing it to an /ɛ/, which explains why the plural of “man” is “men”.
    Other than when forming plural nouns, “I-umlaut” distinguishes several related forms of words. For example, in the past tense form of some verbs like “fall vs fell”. The verb “feed” is part of a class of verbs in Old English derived from nouns with the archaic verbal suffix -ian (pronounced as one syllable, like “Yahn”). So the verb “feed” would have a progression like this: *fod-ian > fød-ian > fed-ian > fed, the same vowel changes as the word “tooth”, but in this case not because of the Proto-English plural marker *-iz but because of the verbal suffix -ian, which was subsequently lost. “I-mutation” also effects the comparative and superlative forms of some adjectives. The comparative form of the adjective is the form of the adjective with the suffix “-er” in Modern English, where is the adjective means “X”, then the comparative form of the adjective means “more X”, and the superlative form has the “-est” suffix and Modern English, which means “the MOST X”. For example, compare “old, elder, eldest”. The comparative form was made with the suffix *-ira in Proto English, and the superlative with *-ist. So the “o” in “old” was fronted to an “e” because of the /i/ sound in the following syllable. The last important example of “I-mutation” in Modern English concerns abstract nouns (nouns not referring to concrete material objects like “ball” but abstract concepts like “justice” and “peace”) that were formed from adjectives with the -th suffix. For example, “long vs length” and “strong vs strength”. In these cases, the adjective form (long and strong ) was the original word, and the noun was derived from the adjective by the addition of the *-itho suffix, which was reduced to a *-th suffix in Old English. So the changes would go like this: *long-itho > *leng-itho > length.
    These two sound changes (Trisyllabic laxing and I-umlaut) should explain almost all discrepancies between the vowels in related forms of words.


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