180. The dental sibilant

Conversion of स् s to ष् ṣ.

The dental sibilant स् s is changed to the lingual ष् ṣ, if immediately preceded by any vowel save अ a and आ ā, or by क् k or र् r—unless the स् s be final, or followed by र् r.

a. The assimilating influence of the preceding lingual vowels and semivowel is obvious enough; that of k and the other vowels appears to be due to a somewhat retracted position of the tongue in the mouth during their utterance, causing its tip to reach the roof of the mouth more easily at a point further back than the dental one.

b. The general Hindu grammar prescribes the same change after a l also; but the Prātiçākhyas give no such rule, and phonetic considerations, the l being a dental sound, are absolutely against it. Actual cases of the combination do not occur in the older language, nor have any been pointed out in the later.

c. The vowels that cause the alteration of s to ṣ may be called for brevity’s sake “alterant” vowels.