As discussed below, the most significant form of mutation in the history of English was the i-mutation (also known as front mutation). This system of changes occurred before the appearance of written Old English (probably in the sixth century) and no longer plays an important role in modern English.
Examples and Observations:
- "In English, the results of i-mutation can be seen in:
(a) the plurals of seven nouns (foot, goose, louse, man, mouse, tooth, woman) which are sometimes called mutation pluralsThis cannot be considered to have a live functional role in modern English, however."
(b) the comparative and superlative elder, eldest
(c) derivative verbs such as bleed (beside blood), fill (beside full), heal (beside whole), etc.
(d) derivative nouns such as breadth (beside broad), length (beside long), filth (beside foul), etc.
(Sylvia Chalker and Edmund Weiner, Oxford Dictionary of English Grammar. Oxford University Press, 1994)
- "Less clearly to be counted as examples of mutation might be the noun-verb conversion pairs of English that involve a stress shift: pro ́duceN ~ produ ́ceV; pe ́rmitN ~ perm ́ıtVV; etc. . . . Are these to be treated as items involving substitution of segments or features?"
(G. E. Booij, Christian Lehmann, and Joachim Mugdan, Morphologie/Morphology: Ein Internationales Handbuch. Walter de Gruyter, 2000)
- Plurals Formed by Mutation
"In a few nouns, the plural is formed by mutation (a change in the vowel):
man/menChildren, the plural of child, combines a vowel change and the irregular ending -en (a survival of an Old English plural inflection). A similar combination appears in brethren, a specialized plural of brother. The older plural ending is found without vowel change in ox/oxen. In American English there are also variant plurals of ox: oxes and the unchanged form ox."
(Sidney Greenbaum, Oxford English Grammar. Oxford University Press, 1996)
- What Is "I-Mutation"?
"Early in the history of English a rule called i-Mutation (or i-Umlaut) existed that turned back vowels into front vowels when an /i/ or /j/ followed in the next syllable. For example in a certain class of nouns in the ancestor of Old English, the plural was formed not by adding -s but by adding -i. Thus the plural of /gos/ 'goose' was /gosi/ 'geese.' . . . [T]he i-Mutation is an example of a rule that was once present in Old English but has since dropped out of the language, and thanks to the Great Vowel Shift even the effects of i-Mutation have been altered."
(Adrian Akmajian, Richard A. Demers, Ann K. Farmer, and Robert M. Harnish, Linguistics: An Introduction to Language and Communication, 5th ed. MIT Press, 2001)
"In prehistoric Old English a number of combinative sound changes took place. One with far-reaching effects was front mutation or i-umlaut (also known as i-mutation). This was a series of changes to vowels which took place when there was an i, ī or j in the following syllable. Subsequently, the i, ī or j disappeared, or changed to e, but its original presence can be established by examining the cognate words in other languages. For example, front mutation accounts for the difference in vowel between the related words dole and deal. In Old English they are dāl 'portion' and dǣlan 'to divide, distribute,' in which the ǣ is due to front mutation; this is clear if we look at the cognate Gothic words, which are dails and dailjan (note that the sound spelt ai in the Gothic words regularly becomes ā in Old English before front mutation takes place; the i in these spellings could not cause front mutation itself). . . .
"The change from ā to ǣ was a movement to a closer and more frontal vowel, and this is the general direction of the changes caused by front mutation: it was obviously a kind of assimilation, the affected vowels being moved to a place of articulation nearer to that of the following vowel or j. Thus ū became fronted to y, a change which accounts for the different vowels of mouse and mice, which have developed regularly from OE mūs, mys; the original plural form was *mūsiz, but the i caused the ū to change to y; then the ending *-iz was lost, giving the OE plural mys.
"Similarly, front mutation changed short u to y; this change is reflected in the different vowels of full and fill, which in Old English are full and fyllan (from earlier *fulljan)."
(Charles Barber, Joan Beal, and Philip Shaw, The English Language, 2nd ed. Cambridge University Press, 2009)
"I-mutation, which caused stem vowel alternation in the word classes substantive and adjective, affected verbs, too. In OE strong verbs, the second and third person singular indicative present was not only marked by special endings but also by i-mutation of the stem vowel, e.g. ic helpe, þu hilpst, he hilpþ; ic weorpe, þu wierpst, he wierpþ; ic fare, þu faerst, he faerþ . . .. This stem alternation was given up in ME."
(Lilo Moessner, Diachronic English Linguistics: An Introduction. Gunter Narr Verlag, 2003)