In some cases, assimilation causes the sound spoken to differ from the normal pronunciation in isolation, such as the prefix in- of English input pronounced with phonetic [m] rather than [n].
In other cases, the change is accepted as canonical for that word or phrase, especially if it is recognized in standard spelling: implosion pronounced with [m], composed of in- + -plosion (as in explosion).
English "handbag" (canonically /ˈhændbæɡ/) is often pronounced /ˈhæmbæɡ/ in rapid speech because the [m] and [b] sounds are both bilabial consonants, and their places of articulation are similar.
However, the sequence [d]-[b] has different places but similar manner of articulation (voiced stop) and is sometimes elided, which sometimes causes the canonical [n] phoneme to assimilate to [m] before the [b].
[note 4] Assimilation can be synchronic, an active process in a language at a given point in time, or diachronic, a historical sound change.
In assimilation, the phonological patterning of the language, discourse styles and accent are some of the factors contributing to changes observed.
On the rare occasion that Italian /kt/ is encountered, however, the same assimilation that triggered the restructuring can occur at the phonetic level.
For example, the medical term ictus 'stroke', a relatively recent direct borrowing from Latin, is usually pronounced [ˈiktus] in deliberate speech, but [ˈittus] is frequent in more casual registers.
There has been a notable change recognized across a variety of English dialects regarding the pronunciation of the /tr/ and /dr/ consonant clusters.
Starting around the mid-20th century,[4] the alveolar stop in /tr, dr/ has slowly been replaced by a post-alveolar affricate instead, resulting in the all-postalveolar consonant clusters [tʃɹ] and [dʒɹ].
[5] One of the first papers that discussed the affrication of /tr, dr/ is "Pre-School Children's Knowledge of English Phonology" by Charles Read, published in 1971.
[6] The study discussed in this paper focuses on how children in pre-school analyze the phonetic aspect of language in order to determine the proper spelling of English words.
For example, in the history of English, a back vowel became front if a high front vowel or semivowel (*i, ī, j) was in the following syllable, and a front vowel became higher unless it was already high: On the other hand, Proto-Germanic *i and *u > e, o respectively before *a in the following syllable (Germanic a-mutation) although that had already happened significantly earlier: Another example of a regular change is the sibilant assimilation of Sanskrit in which if there were two different sibilants as the onset of successive syllables, a plain /s/ was always replaced by the palatal /ɕ/: Lag assimilation to an adjacent segment[3] is tolerably common and often has the nature of a sound law.
In Polish, /v/ regularly becomes /f/ after a voiceless obstruent: This does not apply across word boundaries, so that the placename Grodzisk Wielkopolski is pronounced [ˈɡrɔdʑizɡ vjɛlkɔˈpɔlskʲi], not [ˈɡrɔdʑisk fjɛlkɔˈpɔlskʲi].
Because of a similar process, Proto-Indo-Iranian *ćw became sp in Avestan: Old Avestan aspa 'horse' corresponds to Sanskrit aśva Lag assimilation at a distance is rare and usually sporadic (except when part of a broader change, as for the Sanskrit śaśa- example, above): Greek leirion > Lat.