226. In general

In general, final lingual ष् ṣ, in internal combination, is treated in the same manner as palatal श् ç. Thus:

a. Before t and th it remains unchanged, and the latter are assimilated: e.g. dviṣṭas, dviṣṭhas, dvéṣṭum.

This is a common and perfectly natural combination.

b. Before dh, bh, and su, as also in external combination (145), it becomes a lingual mute: and dh is made lingual after it: e.g. piṇḍḍhi, viḍḍhi, viviḍḍhi, dviḍḍhvam, dviḍbhís, dviṭsú; bhinnaviṭka.

c. So also the dh of dhvam as ending of 2d pl. mid. becomes ḍh after final ṣ of a tense-stem, whether the ṣ be regarded as lost or as converted to ḍ before it (the manuscripts write simply ḍhv, not ḍḍhv; but this is ambiguous: see 232). Thus, after ṣ of s-aorist stems (881 a), astoḍhvam, avṛḍhvam, cyoḍhvam (the only quotable cases), from astoṣ + dhvam etc.; but arādhvam from arās + dhvam. Further, after the ṣ of iṣ-aorist stems (901 a), āindhiḍhvam, artiḍhvam, ajaniḍhvam, vepiḍhvam (the only quotable cases), from ajaniṣ + dhvam etc. Yet again, in the precative (924), as bhaviṣīḍhvam, if, as is probable (unfortunately, no example of this person is quotable from any part of the literature), the precative-sign s (ṣ) is to be regarded as present in the form. According, however, to the Hindu grammarians, the use of ḍh or of dh in the iṣ-aorist and precative depends on whether the i of iṣ or of iṣī is or is not “preceded by a semivowel or h”—which both in itself appears senseless and is opposed to the evidence of all the quotable forms. Moreover, the same authorities prescribed the change of dh to ḍh under the same restriction as to circumstances, in the perf. mid. ending dhve also: in this case, too, without any conceivable reason; and no example of ḍhve in the 2d pl. perf. has been pointed out in the literature.

d. The conversion of ṣ to ṭ (or ḍ) as final and before bh and su is parallel with the like conversion of ç, and of j and h in the mṛj and ruh classes of roots, and perhaps with the occasional change of s to t (167–8). It is a very infrequent case, occurring (save as it may be assumed in the case of ṣaṣ) only once in the RV. and once in the AV. (-dviṭ and -pruṭ), although those texts have more than 40 roots with final ṣ; in the Brāhmaṇas, moreover, have been noticed further only -pruṭ and víṭ (ÇB.), and -çliṭ (K.). From piṅṣ, RV. has the anomalous form piṇak (2d and 3d sing., for pinaṣ-s and pinaṣ-t).

e. Before s in internal combination (except su of loc. pl.) it becomes k: thus, dvékṣi, dvekṣyā́mi, ádvikṣam.

f. This change is of anomalous phonetic character, and difficult of explanation. It is also practically of very rare occurrence. The only RV. examples (apart from piṇak, above) are vivekṣi, from √viṣ, and the desid. stem ririkṣa from √riṣ; AV. has only dvikṣat and dvikṣata, and the desid. stem çiçlikṣa from √çliṣ. Other examples are quotable from √√kṛṣ and piṣ and viṣ (ÇB. etc.), and çiṣ (ÇB.); and they are by the Hindu grammarians prescribed to be formed from about half-a-dozen other roots.