Vowel hiatus or dieresis refers to a sequence of two adjacent vowels that belong to separate syllables and there is no consonant sound between them. In some languages including Persian, the rules of how sounds are placed next to each other does not allow vowel hiatus. Persian resolves vowel hiatus by adding an extra consonant between adjacent vowels. This action is called epenthesis and the extra consonant is called an epenthetic consonant. The epenthetic consonant is often “y”, sometimes “ø” and in certain cases, “v” or “h”.

Persian’s syllable pattern is CV(C)(C). The following table shows all possible combinations for two adjacent syllables. In all cases, adjacent syllables never form V-V. This clearly proves that Persian disallows vowel hiatus.

CV CVC CVCC
CV CV-CV CV-CVC CV-CVCC
CVC CVC-CV CVC-CVC CVC-CVCC
CVCC CVCC-CV CVCC-CVC CVCC-CVCC

Epenthesis in the interior of a word

There are two main spelling candidates for the word سیاه: “siâh” and “siyâh”. The first candidate breaks into the syllables si-âh and the second candidate breaks into si-yâh. Given that Persian disallows vowel hiatus, the correct spelling is siyâh. In languages like Spanish, it is possible to say Espania but in Persian, “es-pa-ni-â” is not possible and this country is spelled and pronounced as “Espâniyâ” (اسپانیا). More examples: “biyâbân” (desert), “khiyâr” (cucumber), “piyâz” (onion), “pâyiz” (fall, autumn).

In Arabic loanwords whose vowels are separated by a glottal stop, there is a tendency to replace glottal stop with the consonant “y”. For instance, رئیس is the original spelling but it is commonly written as رییس and is pronounced “ra-yis” instead of “ra-øis”.

Epenthesis at word boundaries

When a prefix ending in a vowel is added to a word beginning with a vowel, an epenthesis occurs. The epenthetic consonant is “ø” for the vowels “i” and “u” and for other vowels, a “y” is added. When the epenthetic consonant is “ø” (hamze, glottal stop), it does not appear in writing because in Persian, vowels at the beginning of a syllable are naturally articulated with a hamze, making it redundant to write “ø”. The following table shows some examples with the negation prefix na- and the imperfect prefix mi-.

Without Prefix With Prefix “na-” With Prefix “mi-”
آمدم
âmadam
I came
نیامدم
nayâmadam
I did not came
می‌آمدم
miâmadam
I used to come
افتادم
oftâdam
I fell
نیفتادم
nayoftâdam
I did not fall
می‌افتادم
mioftâdam
I used to fall
ایستادم
istâdam
I stood
نایستادم
naistâdam
I did not stand
می‌ایستادم
miistâdam
I used to stand

When a suffix beginning with a vowel is added to a word ending in a vowel, an epenthesis occurs. The epenthetic consonant is either “y” or “ø”. When it is a glottal stop, it does not appear in writing. The following table shows “gu”, the present stem of the verb “goftan”, in combination with different suffixes.

می‌گویم
miguyam
I say
“gu-” + conjugational ending “-am”
گویش
guyesh
dialect
“gu-” + derivational suffix “-esh”
گوینده
guyande
speaker, announcer
“gu-” + derivational suffix “-ande”
گویا
guyâ
speaking, evident
“gu-” + derivational suffix “-â”

Epenthesis between words

The English indefinite article “a” becomes “an” before a vowel. This is an example of epenthesis between words. The Spanish conjunction “y” (and) becomes “e” when it precedes a word that begins with the /i/ sound. Persian has also examples of epenthesis between words.

The indefinite article “i” becomes “yi” after the vowels “â”, “o” and “u”.

صدایی
sedâ-yi
a sound

The genitive marker “e” becomes “ye” after vowels.

چشمهای سارا
cheshmhâ-ye Sârâ
the eyes of Sarah

The conjunction “o” (and) becomes “vo” after the vowel “â” and “yo” after the vowel “i”.

ما و شما
mâ vo shomâ
you and us
علی و پیمان
Ali yo Peymân
Ali and Peyman

In spoken Persian, the dative preposition “به” (be) is combined with bound personal pronouns. The epenthetic consonant is “h” in this case.

بهم
behem
to me
بهمون
behemun
to us
بهت
behet
to you
بهتون
behetun
to you
بهش
behesh
to him/her/it
بهشون
beheshun
to them