184. The principle cases of alteration

The principle cases of alteration of s in internal combination are these:

a. In endings, inflectional or derivative, beginning with s—thus, su; si, se, sva; s of sibilant-aorist, future, and desiderative; suffixes sna, snu, sya, etc.—after a final alterant vowel or consonant of root or stem, or a union-vowel: thus, juhoṣi, çeṣe, anāiṣam, bhaviṣyāmi, çuçrūṣe, deṣṇa, jiṣṇu, vikṣu, akārṣam.

b. The final s of a stem before an ending or suffix: thus: haviṣā, haviṣas, etc., from havis; çakṣuṣmant, çociṣka, mānuṣa, manuṣya, jyotiṣṭva.

c. Roots having a final sibilant (except ç) after an alterant vowel are—with the exception of fictitious ones and pis, niṅs, hiṅs—regarded as ending in ṣ, not s; and concerning the treatment of this ṣ in combination, see below, 225–6.

d. The initial s of a root after a reduplication: thus, siṣyade, suṣvāpa, sīṣāsati, coṣkūyate, saniṣvaṇat.

e. Excepted is in general an initial radical s in a desiderative stem, when the desiderative-sign becomes ṣ: thus, sisīrṣati from √sṛ, sisan̄kṣati from √sañj. And there are other scattering cases, as tresus (perf. from √tras), etc.