# Fusion (phonetics)

In phonetics and historical linguistics, fusion, or coalescence, is a sound change where two or more segments with distinctive features merge into a single segment. This can occur both on consonants and in vowels. A word like educate is one that may exhibit fusion, e.g. /ˈɛdjʊkeɪt/ or /ˈɛdʒʊkeɪt/. A merger between two segments can also occur between word boundaries, an example being the phrase got ya /ˈɡɒt jə/ being pronounced like gotcha /ˈɡɒtʃə/. Most cases of fusion lead to allophonic variation, though some sequences of segments may lead to wholly distinct phonemes.
A common form of fusion is found in the development of nasal vowels, which frequently become phonemic when final nasal consonants are lost from a language. This occurred in French and Portuguese. Compare the French words un vin blanc "a white wine" with their English cognates, one, wine, blank, which retain the n's.
Often the resulting sound has the place of articulation of one of the source sounds and the manner of articulation of the other, as in Malay.
Vowel coalescence is extremely common. The resulting vowel is often long, and either between the two original vowels in vowel space, as in [ai] → [eː] → [e] and [au] → [oː] → [o] in French (compare English day [deɪ] and law [lɔː]), in Hindi (with [ɛː], [ɔː]), and in some varieties of Arabic; or combines features of the vowels, as in [ui] → [yː] → [y] and [oi] → [øː] → [ø].
Compensatory lengthening may be considered an extreme form of fusion.

## Examples
### Indo-European languages
#### English

Historically, the alveolar plosives and fricatives have fused with /j/, in a process referred to as yod coalescence. Words like nature and omission have had such consonant clusters, being pronounced like /naːˈtiu̯r/ and /ɔˈmisjən/. Words ending in the Latin-derived suffixes -tion and -sion, such as fiction and mission, are examples that exhibit yod coalescence.
This sound change was not, however, distributed evenly. Words like module may be realised as either /ˈmɒdjuːl/ or /ˈmɒdʒuːl/. Words that did not experience universal yod coalescence, are always realised as two segments in accents like Received Pronunciation. Most other dialects do pronounce them as one segment, however, like American English.
Words with primary stress on a syllable with such a cluster did not experience coalescence either. Examples include tune /tjuːn/ and assume /əˈsjuːm/. Some dialects exhibit coalescence in these cases, where some coalesce only /tj/ and /dj/, while others also coalesce /sj/ and /zj/. In General American, /j/ elides entirely when following alveolar consonants, in a process called yod dropping. The previous examples end up as /tuːn/ and /əˈsuːm/. Words that have already coalesced are not affected by this.
Australian English exhibits yod coalescence to an extreme degree, even when the cluster is in a stressed syllable, though there is some sociolectal variation. In an accent with full yod coalescence, tune and assume are pronounced like /tʃuːn/ and /əˈʃuːm/. This can result in homophony between previously distinct words, as between dune and June, which are both pronounced /d͡ʒuːn/.

#### Romance languages

Most Romance languages have coalesced sequences of consonants followed by /j/. Sequences of plosives followed by /j/ most often became affricates, often being intermediary stages to other manners of articulation. Sonorants in such a sequence (except bilabial consonants) mostly became palatalized.

#### Greek

During the development of Ancient Greek from Proto-Greek, the labiovelar [kʷ], [kʷʰ], and [ɡʷ] became [p], [pʰ], and [b]. Although the labiovelars were already a single consonant, they had two places of articulation, a velar articulation and labial secondary articulation ([ʷ]). However, the development of labiovelars varies from dialect to dialect, and some may have become dental instead. An example is the word boûs "cow" from Proto-Greek *gʷous.
A vowel coalescence from Ancient Greek to Koine Greek fused many diphthongs, especially those including /i̯/. E.g. /ai̯/ > /e/; /aːi̯/ > /a/; /ɛːi̯/ and /oi̯/ > /i/ and /ɔːi̯/ > /o/.

#### Celtic languages

Several consonant clusters in Proto-Celtic underwent fusion, most prominently /*ɡ/ to the following consonant in coda position. Examples include *ougros to úar and *maglos to mál in Old Irish.

#### North Germanic languages

In Norwegian and Swedish, this process occurs whenever the phoneme /ɾ/ is followed by an alveolar consonant. The articulation of the resulting fusion becomes retroflex. Examples include the Norwegian bart [bɑʈ] and Swedish nord [nuːɖ]. This even occurs across word boundaries, as in the sentence "går det bra?" becoming /ɡoː‿ɖə brɑː/.
This process will continue for as long as there are more alveolar consonants, though when this amount exceeds four, people usually try to break it up or shorten it, usually by replacing /ʂ/ with /s/, or eliding /d/. An extreme example of this would be the word ordensstraff /ɔ.ɖɳ̩ʂ.ʂʈɽɑfː/, having six retroflex consonants in a row.
In colloquial Norwegian, the sequence /rt/ may even coalesce over non-alveolar phonemes, changing their place of articulation to retroflex, even if /r/ normally wouldn't trigger it. Examples include sterkt /stæɾkt/ [stæʈː], skarpt /skɑɾpt/ [skɑʈː], verktøy /ʋæɾk.tœʏ̯/ [ʋæʈ.ʈœʏ̯] and varmt /ʋɑɾmt/ [ʋɑɳʈ]. This process does not occur across word boundaries, e.g. sterk tann is pronounced /stæɾk tɑnː/ and not */stæ‿ʈɒnː/
In dialects where /r/ is articulated uvularly, this process invariably takes place on idiolectal level. For example, /rɑːrt/ may be realised as [ʁɑːʁt] or [ʁɑːʈ]. This may appear in regions where /r/ has recently become uvular.

### Austronesian languages
#### Malay

In Malay, the final consonant of the prefix /məN-/ (where N stands for a "placeless nasal", i.e. a nasal with no specified place of articulation) coalesces with a voiceless stop at the beginning of the root to which the prefix is attached. The resulting sound is a nasal that has the place of articulation of the root-initial consonant. For example:
* /məN + potoŋ/ becomes /məmotoŋ/ 'cut' ([p] and [m] are both pronounced with the lips)
* /məN + tulis/ becomes /mənulis/ 'write' ([t] and [n] are both pronounced with the tip of the tongue)
* /məN + kira/ becomes /məŋira/ 'guess' ([k] and [ŋ] are both pronounced at the back of the tongue)

### Japanese

Vowel coalescence occurs in Owari Japanese. The Diphthongs /ai/ and /ae/ change to [æː], /oi/ and /oe/ change to [øː] and /ui/ changes to [yː]. E.g. 来年 /raineN/ > [ræ:nen], 鯉 /koi/ > [køː], 熱い /atsui/ > [atsyː~atɕːyː]. Younger speakers may vary between Standard Japanese diphthongs and dialectal monophthongs.