Assimilation is a common phonological
process by which the phonetics of a speech segment becomes
more like that of another segment in a word (or at a word
boundary). A common example of assimilation would be "don't
be silly" where the /n/
in "don't" become /m/
where said naturally in many accents and discourse styles
("dombe silly"). Assimilation can be synchronic
being an active process in a language at a given point
in time or diachronic
being a historical sound
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 /b/
becoming labialised as in "boot". This article will describe
both processes under the term, assimilation.
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:
the increase in phonetic similarity may be between adjacent
segments, or between segments separated by one or more
intervening segments; and the changes may be in reference
to a preceding segment, or to a following one. Although
all four occur, changes in regard to a following adjacent
segment account for virtually all assimilatory changes
(and most of the regular ones). Also, 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
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.
Very 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
Some authorities distinguish between partial and complete
assimilation, i.e., between assimilatory changes in which
there remains some phonetic difference between the segments
involved, and those in which all differences are obliterated.
There is no theoretical advantage to such a classification,
as one of the following examples will show.
languages may exhibit tone assimilation (tonal umlaut,
in effect), while sign
languages also exhibit assimilation when the characteristics
of neighbouring phonemes 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. Thus in
Latin, prefixes ending in a nasal (com- "with"
(also marks completive action); in- "in(to)" (also
marks "ingression", i.e. the commencement of an action);
in- (forms privative adjectives)) all show the
following assimilatory changes relative to a following
All become /m/
impendeō "hang over", imbibō "drink in", immēnsus
"immeasurable" All become /n/
contāminō "render unclean", connīveō
"lower the eyes; be complicit', condōnō "give
away, present" All become /l/
respectively: corrumpō "break to pieces", irrētiō
"entangle in a net", irrāsus "unshaved", illūdō
"play with", illīterātus "ignorant, unlettered",
colloquor "converse, talk with", collūdō "play
with" (but usually "have a secret understanding with").
The assimilation to [ŋ]
is not shown in writing.
Also in Latin, a stop followed by a nasal assimilates
to the nasal: Proto-Indo-European *swepnos "sleep"
> Lat. somnus [the vowel changes are regular,
too], *supmos "highest" > summus, *ad-nec-
> annectō "bind to" (cf. annex),
sub-moenium "red light district" (lit. "under the
walls") > summoenium. (This example also indicates
the pointlessness of the division into "partial" and "complete"
assimilations: this is plainly a single sound-law—stops
become nasals—and whether the output assimilation is "complete"
or "partial" hinges inconsequentially on the phonetic
details of the input.)
In Italian, voiceless stops assimilate to a following
Latin okto "eight" > It. otto, Latin
lectus "bed" > letto, suptus "under"
Anticipatory assimilation at
Rare, and usually merely an accident in the history of
a specific word. Old French cercher "to chase"
> Modern Fr. chercher /ʃɛʁ.ʃe/.
However, the diverse and common assimilations known as
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 /s/
was always replaced by the palatal /ɕ/:
Proto-Indo-European *smeḱru- "beard" >
Skt. śmaśru-; *ḱoso- "gray"
> Skt. śaśa- "rabbit"; PIE *sweḱru-
"husband's mother' > Skt. śvaśrū-.
Lag assimilation to a contiguous
Tolerably common, and often has the nature of a sound
law. Proto-Indo-Eruopean *-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
harmony is the reverse of umlaut, namely, a following
vowel's phonetics is influenced by that of a preceding
vowel. Thus for example most Finnish case markers come
in two flavors, with /a/
(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
Proto-Italic *dw > Latin b, as in *dwis
"twice" > Lat. bis. 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 /f/:
má fiur "my sister", bó tri-fne
"a cow with three teats". There's also the famous change
of kW -> p. Proto-Celtic
also underwent the change gw -> b.
- Crowley, Terry. (1997) An Introduction to Historical
Linguistics. 3rd edition. Oxford University Press.