**Epenthesis** is a term in phonology. It refers to adding one or more sounds to a word. 

If it is added at the beginning, it is called *prothesis*. If added at the end of the word, it is called *paragoge*. There are two types of epenthesis: when a consonant is added, and when a vowel is added. The opposite process where one or more sounds are removed is called **elision**.

Uses
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Epenthesis can happen for many reasons. The rules of how sounds are placed in a language may not allow vowels next to each other, but in different syllables. Some consonant clusters may not be allowed. In this situation a consonant or vowel can be added to make pronunciation easier. Epenthesis may be shown in writing or may happen in spoken language.

### Separating vowels

A consonant can be added to separate spoken vowels in hiatus. This happens with linking and intrusive R, which is a rule that puts an 'r' in a place where it doesn't normally happen.

* *drawing* → *draw**r**ing* (in speech).

### Linking consonant clusters

A consonant can be placed between consonants in a consonant cluster where the place of articulation is different (e.g. where one consonant is labial (pronounced with the lips) and the other is alveolar. 

* *something* → *some**p**thing* (but not in standard English).

### Breaking consonant clusters

A vowel can be placed between consonants to separate them.

* *Hamtramck* → *Hamtram**i**ck*

Regular examples in English are *-i-*, used in making words from Latin such as *equ**i**distant*, and *-o-*, used in making words from Greek roots or general compound words, as in *speed**o**meter*.

### Sound change in history

* Latin *tremulare* > French *trembler* ("to tremble")
* Old English *thunor* > English *thunder*
* French *messager*, *passager* > English *messenger*, *passenger*
* French *message*, *messager* > Portuguese *mensagem*, *mensageiro*
* Latin *homine(m)* > *homne* > *homre* > Spanish *hom**b**re* ("man")

### Rules in present-day languages

In French, /t/ is placed in inverted interrogative phrases between a verb that ends in a vowel and a pronoun that begins with a vowel: *il a* ('he has') > *a-t-il* ('has he?').  Because the *a-t* come from Latin *habet* ('he has') there is no epenthesis from the point of view of history. This is because the *t* is the original third-person verb inflection. However it is correct to call it epenthesis in the modern language because the modern basic form of the verb is *a*, so the way the process works in the mind is to add a *t* to the basic form.

A similar example is the English indefinite article *a*, which becomes *an* before a vowel. It comes from Old English *ān* ("one, a, an"), which kept an *n* in all positions. From a diachronic (historical) analysis, the original *n* disappears, except if a following vowel needs for it to stay: *an* > *a*. However, with a synchronic analysis people can also see it as epenthesis: *a* > *an*. This is how most native speakers see it.

In Dutch, when the suffix *-er* (which has several meanings) is placed after a word which already ends in *-r*, another *-d-* is put in the middle. For example, the comparative form (the form people use to compare things) of the adjective *zoet* ("sweet") is *zoeter*, but the comparative of *zuur* ("sour") is *zuur**d**er* and not the expected \**zurer*. The same happens with the agent (someone who does something) noun form of *verkopen* ("to sell") which is *verkoper* ("salesperson"), but the agent noun of *uitvoeren* ("to perform") is *uitvoer**d**er* ("performer").

### Variable rule

In English, people often add a stop consonant in nasal + fricative combinations:

* English *hamster* /ˈhæmstər/often pronounced with an added *p* sound, GA: [ˈhɛəmpstɚ] or RP: [ˈhampstə]
* English *warmth* /ˈwɔːrmθ/  often pronounced with an added *p* sound, GA: [ˈwɔɹmpθ] or RP: [ˈwoːmpθ]
* English *fence* /ˈfɛns/  often pronounced [ˈfɛnts]

Sources
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* Crowley, Terry. (1997) *An Introduction to Historical Linguistics.* 3rd edition. Oxford University Press.

Other websites
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* Definition at BYU