Assimilation (linguistics)

Assimilation is a common phonological process by which one sound becomes more like a nearby sound. This can occur either within a word or between words. In rapid speech, for example, "handbag" is often pronounced [ˈhambag], and "hot potato" as [ˈhɒppəteɪtoʊ]. As in these two examples, sound segments typically assimilate to a following sound (this is called regressive or anticipatory assimilation), but they may also assimilate to a preceding one (progressive assimilation). While assimilation most commonly occurs between immediately adjacent sounds, it may occur between sounds separated by others ("assimilation at a distance").

Assimilation can be synchronic&mdash; that is, an active process in a language at a given point in time&mdash; or diachronic: That is, a historical sound change.

A related process is coarticulation where one segment influences another to produce an allophonic variation, such as vowels acquiring the feature nasal before nasal consonants when the velum opens prematurely or becoming labialised as in "boot". This article will describe both processes under the term, assimilation.

Concept
The physiological or psychological mechanisms of coarticulation are unknown, but we often loosely speak of a segment as "triggering" an assimilatory change in another segment. In assimilation, the phonological patterning of the language, discourse styles and accent are some of the factors contributing to changes observed.

There are four configurations found in assimilations:
 * Between adjacent segments.
 * Between segments separated by one or more intervening segments.
 * Changes made in reference to a preceding segment
 * Changes made in reference to a following segment

Although all four occur, changes in regard to a following adjacent segment account for virtually all assimilatory changes (and most of the regular ones). Assimilations to an adjacent segment are vastly more frequent than assimilations to a non-adjacent one. These radical asymmetries might contain hints about the mechanisms involved, but they are unobvious.

If a sound changes with reference to a following segment, it is traditionally called "regressive assimilation"; changes with reference to a preceding segment are traditionally called "progressive". Many find these terms confusing, as they seem to mean the opposite of the intended meaning. Accordingly, a variety of alternative terms have arisen—not all of which avoid the problem of the traditional terms. Regressive assimilation is also known as right-to-left, leading, or anticipatory assimilation. Progressive assimilation is also known as left-to-right or perseveratory or preservative, lagging or lag assimilation. The terms anticipatory and lag will be used here.

Occasionally two sounds (invariably adjacent) may influence one another in reciprocal assimilation. When such a change results in a single segment with some of the features of both components, it is known as coalescence or fusion.

Some authorities distinguish between partial and complete assimilation; that is, between assimilatory changes in which there remains some phonetic difference between the segments involved, and those in which all differences are obliterated.

Tonal languages may exhibit tone assimilation (tonal umlaut, in effect), while sign languages also exhibit assimilation when the characteristics of neighbouring cheremes may be mixed.

Anticipatory assimilation to a contiguous segment
This is the most common type of assimilation by far, and typically has the character of a conditioned sound change, i.e., it applies to the whole lexicon. For example, in English, the place of articulation for nasal consonants assimilates to that of a following stop consonant (bank is pronounced, handbag in rapid speech is pronounced ). In Italian, voiceless stops assimilate to a following : Latin okto "eight" > It. otto, Latin lectus "bed" > letto, suptus "under" > sotto.

Anticipatory assimilation at a distance
Rare, and usually merely an accident in the history of a specific word. Old French cercher "to search" > Modern Fr. chercher. However, the diverse and common assimilations known as umlaut, wherein the phonetics of a vowel are influenced by the phonetics of a vowel in a following syllable, are both commonplace and in the nature of sound laws. Such changes abound in the histories of Germanic Languages, Romanian, Old Irish, and many others. Examples: in the history of English, a back vowel becomes front if a high front vocoid (*i, ī, y) is in the following syllable: Proto-Germanic *mūsiz "mice" > Old English mýs > mice; PGmc *batizōn- "better" > OE bettre; PGmc *fōtiwiz "feet" > OE fét > feet. Contrariwise, Proto-Germanic *i and *u > e, o respectively before *a in the following syllable: PGmc *nistaz > OE nest. Another example of a regular change is the sibilant assimilation of Sanskrit, wherein if there were two different sibilants as the onset of successive syllables, a plain was always replaced by the palatal : Proto-Indo-European *smeḱru- "beard" > Skt. śmaśru-; *ḱoso- "gray" > Skt. śaśa- "rabbit"; PIE *sweḱru- "husband's mother' > Skt. śvaśrū-.

Lag assimilation to a contiguous segment
Tolerably common, and often has the nature of a sound law. Proto-Indo-European *-ln- > -ll- in both Germanic and Italic. Thus *ḱļnis "hill" > PreLat. *kolnis > Lat. collis; > PGmc *hulniz, *hulliz > OE hyll > hill. The enclitic form of English is, shedding the vowel, becomes voiceless when adjacent to a word-final voiceless non-sibilant.

Lag assimilation at a distance
Rare, and usually sporadic (except when part of something bigger, as in the Skt. śaśa- example, above): Greek leirion > Lat. līlium "lily". In vowel harmony, a vowel's phonetics is often influenced by that of a preceding vowel. Thus for example most Finnish case markers come in two flavors, with and  (written ä) depending on whether the preceding vowel is back or front. However, it's a difficult question to know just where and how in the history of Finnish an actual assimilatory change took place. The distribution of pairs of endings in Finnish is just that, is not in any sense the operation of an assimilatory innovation (though probably the outbirth of such an innovation in the past).

Coalescence (fusion)
Proto-Italic *dw > Latin b, as in *dwis "twice" > Lat. bis. Also, Old Latin duellum > Latin bellum "war". Proto-Celtic *sw shows up in Old Irish in initial position as s, thus *swesōr "sister" > OIr siur, *spenyo- > *swinea- > *swine "nipple" > sine. But when a vowel preceded, the *sw sequence becomes : má fiur "my sister", bó tri-fne "a cow with three teats". There is also the famous change in P-Celtic of kW -> p. Proto-Celtic also underwent the change gw -> b.