Sandhi: how sounds join

When two words or word-parts meet, the last sound of the first and the first sound of the second often blend into something new. This blending is सन्धि (sandhi), "joining". विद्या + आलयः becomes विद्यालयः; नमः + ते becomes नमस्ते.

Every language does this in speech: English "do not" becomes "don't". What is special about Sanskrit is that the blending is also written, and written strictly by rule. That is why a line of a shloka looks like one long word. To read it, you must undo the sandhi, a step called सन्धि-विच्छेद (sandhi-vichchheda). Hindi keeps hundreds of Sanskrit sandhi words, so you know many results already: हिमालय, सूर्योदय, इत्यादि, स्वागत, सज्जन.

There are three families: vowel sandhi (स्वर), consonant sandhi (व्यञ्जन) and visarga sandhi (विसर्ग).

Vowel sandhi

1. दीर्घ (dirgha): like vowels make one long vowel

Rule	Example	Result
अ/आ + अ/आ = आ	विद्या + आलयः	विद्यालयः
अ/आ + अ/आ = आ	हिम + आलयः	हिमालयः
इ/ई + इ/ई = ई	कवि + इन्द्रः	कवीन्द्रः
उ/ऊ + उ/ऊ = ऊ	भानु + उदयः	भानूदयः

2. गुण (guna): अ or आ + a different vowel

Rule	Example	Result
अ/आ + इ/ई = ए	देव + इन्द्रः	देवेन्द्रः
अ/आ + उ/ऊ = ओ	सूर्य + उदयः	सूर्योदयः
अ/आ + उ/ऊ = ओ	महा + उत्सवः	महोत्सवः
अ/आ + ऋ = अर्	महा + ऋषिः	महर्षिः

3. वृद्धि (vriddhi): अ or आ + ए, ऐ, ओ, औ

Rule	Example	Result
अ/आ + ए/ऐ = ऐ	सदा + एव	सदैव
अ/आ + ए/ऐ = ऐ	एक + एकम्	एकैकम्
अ/आ + ओ/औ = औ	महा + औषधम्	महौषधम्

4. यण् (yan): इ, उ, ऋ before a different vowel

Rule	Example	Result
इ/ई + other vowel = य्	इति + आदि	इत्यादि
इ/ई + other vowel = य्	यदि + अपि	यद्यपि
उ/ऊ + other vowel = व्	सु + आगतम्	स्वागतम्
ऋ + other vowel = र्	पितृ + आज्ञा	पित्राज्ञा

5. अयादि (ayadi): ए, ऐ, ओ, औ before a vowel

Rule	Example	Result
ए + vowel = अय्	ने + अनम्	नयनम्
ऐ + vowel = आय्	नै + अकः	नायकः
ओ + vowel = अव्	पो + अनः	पवनः
औ + vowel = आव्	पौ + अकः	पावकः

Consonant sandhi: two common cases

A hard consonant softens before a soft sound

Example	Result	What happened
जगत् + ईशः	जगदीशः	त् became द् before a vowel
सत् + जनः	सज्जनः	त् became ज् before ज
वाक् + ईशः	वागीशः	क् became ग् before a vowel
उत् + नतिः	उन्नतिः	त् became न् before न

Visarga sandhi: three common cases

What the visarga (ः) turns into

Example	Result	What happened
नमः + ते	नमस्ते	ः became स् before त
मनः + रथः	मनोरथः	अः became ओ before a soft consonant
सः + अपि	सोऽपि	अः + अ became ओ, and the अ dropped (marked ऽ)
निः + चयः	निश्चयः	ः became श् before च

Undoing sandhi in a shloka

Take the first line of Gita 2.47: कर्मण्येवाधिकारस्ते. It is four words run together. Working backwards: कर्मणि + एव gave कर्मण्येव (yan sandhi: इ before ए became य्); एव + अधिकारः gave एवाधिकारः (dirgha: अ + अ = आ); and अधिकारः + ते gave अधिकारस्ते (visarga became स् before त). So the words are कर्मणि एव अधिकारः ते: "in action alone [is] the right of you".

How to learn sandhi

Start with the five vowel sandhis; they account for most of what you will meet.
For each rule, learn one example you already know from Hindi: विद्यालय, सूर्योदय, सदैव, इत्यादि, नयन.
Practise in both directions: join given pairs, and split given words.
When you read a shloka, mark every ऽ, every long vowel in the middle of a compound and every य् or व् before a vowel: these are the usual signs of a sandhi.

This page gives the main rules in their simplest form. Each rule has exceptions and finer points, which are set out in full in any standard Sanskrit grammar.

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