Apophony

Vowel gradation

Apophony often involves vowels. Indo-European ablaut (English sing-sang) and Germanic umlaut (goose-geese), mentioned above, are well attested examples. Another example is from Dinka:^[1]

The vowel alternation may involve more than just a change in vowel quality. In Athabaskan languages, such as Navajo, verbs have series of stems where the vowel alternates (sometimes with an added suffix) indicating a different tense-aspect. Navajo vowel ablaut, depending on the verb, may be a change in vowel, vowel length, nasality, and/or tone. For example, the verb stem kaah/-ką́ 'to handle an open container' has a total of 16 combinations of the 5 modes and 4 aspects, resulting in 7 different verb stem forms (i.e. -kaah, -kááh, -kaał, -kááł, -ka’, -ká, -ką́).

Another verb stem | -géésh/-gizh 'to cut' has a different set of alternations and mode-aspect combinations, resulting in 3 different forms (i.e. -géésh, -gizh, -gish):

Prosodic apophony

Various prosodic elements, such as tone, syllable length, and stress, may be found in alternations. For example, Vietnamese has the following tone alternations which are used derivationally:^[2]

Albanian uses different vowel lengths to indicate number and grammatical gender on nouns:^[3]

English has alternating stress patterns that indicate whether related words are nouns (first syllable stressed) or verbs (second syllable stressed). This tends to be the case with words in English that came from Latin:^{[citation needed]}

Prosodic alternations are sometimes analyzed as not as a type of apophony but rather as prosodic affixes, which are known, variously, as suprafixes, superfixes, or simulfixes.

Consonant apophony

Consonant alternation is commonly known as consonant mutation or consonant gradation. Bemba indicates causative verbs through alternation of the stem-final consonant. Here the alternation involves spirantization and palatalization:^[4]

Celtic languages are well known for their initial consonant mutations.

Indo-European ablaut

In Indo-European linguistics, ablaut is the vowel alternation that produces such related words as sing, sang, sung, and song. The difference in the vowels results from the alternation (in the Proto-Indo-European language) of the vowel e with the vowel o or with no vowel.

To cite a few other examples of Indo-European ablaut, English has a certain class of verbs, called strong verbs, in which the vowel changes to indicate a different grammatical tense-aspect.

As the examples above show, a change in the vowel of the verb stem creates a different verb form. Some of the verbs also have a suffix in the past participle form.

Umlaut

In Indo-European linguistics, umlaut is the vowel fronting that produces such related words as foot > feet or strong > strength. The difference in the vowels results from the influence of an /i/, /iː/ or /j/ (which in most cases has since been lost) at the end of the word causing the stem vowel to be pulled forward. Some weak verbs show umlaut in the present tense, with the past tense representing the original vowel: bought > buy (/ɔː/>/aɪ/). Hundreds of similar examples can be found in English, German, Dutch and other languages.

Germanic a-mutation is a process analogous to umlaut, but involving the influence of a low vowel such as /ɑ/ causing a high vowel in the stem to lower.

Ablaut versus umlaut

In Indo-European historical linguistics the terms ablaut and umlaut refer to different phenomena and are not interchangeable. Ablaut is a process that dates back to Proto-Indo-European times, occurs in all Indo-European languages, and refers to (phonologically) unpredictable vowel alternations of a specific nature. From an Indo-European perspective, it typically appears as a variation between o, e, and no vowel, although various sound changes result in different vowel alternations appearing in different daughter languages. Umlaut, meanwhile, is a process that is particular to the Germanic languages and refers to a variation between back vowels and front vowels that was originally phonologically predictable, and was caused by the presence of an /i/ or /j/ in the syllable following the modified vowel.

From a diachronic (historical) perspective, the distinction between ablaut and umlaut is very important, particularly in the Germanic languages, as it indicates where and how a specific vowel alternation originates. It is also important when taking a synchronic (descriptive) perspective on old Germanic languages such as Old English, as umlaut was still a very regular and productive process at the time. When taking a synchronic perspective on modern languages, however, both processes appear very similar. For example, the alternations seen in sing/sang/sung and foot/feet both appear to be morphologically conditioned (e.g. the alternation appears in the plural or past tense, but not the singular or present tense) and phonologically unpredictable.

By analogy, descriptive linguists discussing synchronic grammars sometimes employ the terms ablaut and umlaut, using ablaut to refer to morphological vowel alternation generally (which is unpredictable phonologically) and umlaut to refer to any type of regressive vowel harmony (which is phonologically predictable). Ambiguity can be avoided by using alternative terms (apophony, gradation, alternation, internal modification for ablaut; vowel harmony for umlaut) for the broader sense of the words.