EXCEPTIONS OF अयादि-सन्धि

In the following case, this सन्धि is optional:

1. The य् or व् at the end of the word during the occurrence of अयादि-सन्धि in a sentence is optionally dropped.

• हरे + इह = हर इह OR हरयिह।
• तस्मै + अहम् = तस्मा अहम् OR तस्मायहम् । 
• विष्णो + इह = विष्ण इह OR विष्णविह।
• तौ + अतः = ता अतः OR तावतः।   

अयादि-सन्धि - 2

In the following cases, अयादि-सन्धि takes place:

1. ओ or औ when followed by a termination or affix beginning with य् change to अव् or आव् respectively. E.g. Forming word by adding तद्धित affix: गो + यम् = गव्यम्। नौ + यम् = नाव्यम्।This is applicable for roots only when the ओ or औ of the root occurs by change of the ending vowel of the root to गुण or वृद्धि due to the termination that follows. E.g. लू+यम्=लो+यम् = लव्यम्। अवश्यलु+यम्=अवश्यलौ+यम् = अवश्यलाव्यम्। 
2. The ओ of गो is changed to अव् when followed by यूति when it means a particular measure of length. E.g. गव्यूतिः । It is compulsorily changed to अव when followed by इन्द्र or अक्ष - गवेन्द्रः। गवाक्षः। If it is followed by a vowel, it is optionally changed to अव. E.g.गो+अग्रम्=गवाग्रम्, गोऽग्रम् , also गोअग्रम् । गो+उष्ट्रम्=गवोष्ट्रम् or गवुष्ट्रम् ।   
3. The ए of potential participle of roots जि (1 प.) and क्षि (1,5,6 प.) changes to अय् before य when meaning "capable or definitely possible". If it is not definitely possible, the ए remains as it is. E.g. मनः जेयम् (should be conquered but not always possible ); जय्यम् - What can be conquered. पापं क्षेयम् (should be reduced but not always possible) क्षय्यम् - What can be reduced.

अयादि-सन्धि - 1

This सन्धि is the substitution of अय् , आय् , अव् , आव् for ए, ऐ, ओ, औ respectively when followed by any vowel.

• ए + Any vowel = अय्
  E.g.While forming पद - हरे + ए = हरये ।   
• ऐ + Any vowel = आय्
  E.g.In forming word by adding तद्धित (secondary) affix:"अक" - नै + अकः = नायकः ।  
• ओ + Any vowel = अव्
  E.g.While conjugating verb - कृ [8 प.प.] Imperfect past- अकरो + अम् = अकरवम् ।      
• औ + Any vowel = आव्
  E.g.In sentence - भूमौ + आगच्छ = भूमावागच्छ।

पूर्वरूप-सन्धि

When ए or ओ at the end of a word is followed by अ in a sentence, then अ merges with the initial ए or ओ and " ऽ "(अवग्रह) is substituted for अ.

• विष्णो + अव = विष्णोऽव ।
• हरे + अव = हरेऽव ।
• रामः + अवति = रामो + अवति = रामोऽवति ।
  (The change of अः to ओ will be explained later)   

Note : The horizontal stroke is not put over the " ऽ "(अवग्रह). This सन्धि can be said to be an exception of अयादि-सन्धि.