132. In external combination, we have the important additional rule that the semivowel resulting from the conversion of the final element of a diphthong is in general dropped; and the resulting hiatus is left without further change.
133. That is to say, a final ए e (the most frequent case) becomes simply अ a before an initial vowel (except अ a: see 135, below), and both then remain unchanged; and a final ऐ āi, in like manner, becomes (everywhere) आ ā. Thus,
त आगताः ta āgatāḥ (te + āgatāḥ);
नगर इह nagara iha (nagare + iha);
तस्मा अददात् tasmā adadāt (tasmāi + adadāt);
स्त्रिया उक्तम् striyā uktam (striyāi + uktam).
a. The latter grammarians allow the y in such combinations to be either retained or dropped; but the uniform practice of the manuscripts, of every age, in accordance with the strict requirement of the Vedic grammars (Prātiçākhyas), is to omit the semivowel and leave the hiatus.
b. The persistence of the hiatus caused by this omission is a plain indication of the comparatively recent loss of the intervening consonantal sound.
c. Instances, however, of the avoidance of hiatus by combination of the remaining final vowel with the following initial according to the usual rules are met with in every period of the language, from the RV. down; but they are rare and of sporadic character. Compare the similar treatments of the hiatus after a lost final s, 176–7.
d. For the peculiar treatment of this combination in certain cases by the MS., see below, 176 d.
134. a. The diphthong o (except as phonetic alteration of final as: see 175 a) is an unusual final, appearing only in the stem go (361 c), in the voc. sing. of u-stems (341), in words of which the final a is combined with the particle u, as atho, and in a few interjections. In the last two classes it is uncombinable (below, 138 c, f); the vocatives sometimes retain the v and sometimes lose it (the practices of different texts are too different to be briefly stated); go (in composition only) does not ordinarily lose its final element, but remains gav or go. A final as becomes a, with following hiatus, before any vowel save a (for which, see the next paragraph).
