Vowel Sandhi

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This page covers the rules of vowel sandhi. Any rule in which the first letter is a vowel is considered a vowel sandhi rule. If you prefer charts over sentences, you can use the charts at the bottom of the page. As far as I am aware, this page contains every rule of vowel sandhi. Pre-Classical works don't always conform to these rules.

Before you begin

All of the rules below describe changes between two vowels, unless otherwise described. A vowel in front of a consonant will not change, unless otherwise described. The two vowels must be right next to each other with no letters between them.

The basic principle of vowel sandhi

Two vowels should not be next to each other.

Old vowels

Early Sanskrit probably had vowel sounds like you see below:

i, ī*ai*āi
u, ū*au*āu
ṛ, ṝ*ar*ār

A knowledge of these old vowels will simplify the rules below. Over time, the old vowel sounds merged to become the ones we know today:

i, īeai
u, ūoau
ṛ, ṝarār

Similar Vowels

Similar vowels combine and become long. Remember, compound vowels are dissimilar to everything.

Dissimilar Vowels

Two dissimilar vowels will change based on the first vowel.

If the first vowel is -a or , then the first vowel combines with the second and strengthens it by one level. If the second vowel is already strong, then the first vowel disappears.

Otherwise, the first vowel will change to its corresponding semivowel. First, some examples for simple vowels:

Now, some examples for compound vowels. For compound vowels, the second part of the first vowel becomes the semivowel. Remember that e, ai, o, and au are treated as *ai, *āi, *au, and *āu for historical reasons.

Compound vowels have some exceptions in external sandhi.

Special Rules of Internal Sandhi

Simple Vowels

The following simple vowels will frequently change as follows:

First vowel
i, ī
u, ū


, when after a single consonant, becomes ri before y-.

in front of a consonant suffix becomes īr. But if the comes after a letter in pavarga, then it becomes ūr instead. Note that this change applies only when the second letter is a consonant.

Compound Vowels

For compound vowels, the second part of the first vowel becomes the semivowel when it is followed by a vowel. The change also occurs when the second letter is the consonant y. (This change occurs because many of the y consonants in Classical Sanskrit come from i vowels in Vedic Sanskrit.)

Special Rules of External Sandhi

Verb prefixes

A prefix ending in a or ā, when in front of a verb starting with , combines to form ār.

If the verb starts with a vowel, then the a prefix, which is used to mark the past tense, will combine to make the vowel strong.

Also, pra + ūḍha becomes prauḍha.

Compound Vowels

For compound vowels, the second part of the first vowel becomes the semivowel when it is followed by a vowel. But in external sandhi, the semivowel is dropped for e and ai. The next rule features an exception to this one.

When -e is in front of a-, the first vowel stays the same and the a- disappears. Note that the letter a is removed because of the influence of the complex and common e vowel.

Words unaffected by sandhi

The words below will not combine with the words that follow them:

Particles of interjection (he, aho, …) and particles that consist of just a single vowel (ā, i, u, …):

The vowels ī, ū, and e, when they end a word in the dual:

and amī, the plural form of asau.

Other exceptions can be found in Panini's Ashtadhyayi (1.1.11 - 1.1.19; see my translation of these rules here).


External Sandhi

First VowelSecond Vowel
āyavarae 'ā aāvaa
āa āā āāvāā
eīviria iā iāvii
eīa īā īāvīī
oyuūrua uā uāvuu
oūa ūā ūāvūū
aryṛvṛa ṛā ṛāvṛ
aryṝvṝa ṝā ṝāvṝ
aiyeverea eā eāvee
aiyaivairaia aiā aiāvaiai
auyovoroa oā oāvoo
auyauvauraua auā auāvauau