250. But the lightening

But the lightening of a long ā especially to an i-vowel (as also its loss), is a frequent process; no other vowel is so unstable.

a. Of the class-sign nā (of the krī-class of verbs: 717 ff.), the ā is in weak forms changed to ī, and before vowel-endings dropped altogether. The final ā of certain roots is treated in the same manner: thus, mā, hā, etc. (662–6). And from some roots, ā- and ī- or i-forms so interchange that it is difficult to classify them or to determine the true character of the root.

b. Radical ā is weakened to the semblance of the union-vowel i in certain verbal forms: as perfect dadima from √dā etc. (794 k); aorist adhithās from √dhā etc. (834 a); present jahimas from √hā etc. (665).

c. Radical ā is shortened to the semblance of stem-a in a number reduplicated forms, as tiṣṭa, piba, dada, etc.: see 671–4; also in a few aorists, as áhvam, ákhyam, etc.: see 847.

d. Radical ā sometimes becomes e, especially before y: as stheyāsam, deya.