E, and the Vowel That Has No Short Form

Sanskrit has no short e. The vowel is always long, always heavy in metre, and the classical language offers no contrast of quantity for it at all, which sets it apart from the a, i and u series where every vowel has a partner. The reason is historical: e is what an older a and i became when they fell together, and a sound produced by two vowels combining is long by that fact. The grammatical tradition records the outcome by classing e with the compound vowels rather than with the simple ones, which is why it stands after the whole a, i and u sequence in the order instead of beside the front vowels it is made from.

The same combination happens live in the rules of junction. A word ending in a followed by a word beginning in i produces this vowel at the seam, so a reader who meets it in a Sanskrit sentence has to consider whether it belongs to a word or marks the join between two. It is also the first strengthening grade of i, so a root with i shows e whenever a suffix calls for the stronger form, and a great many Sanskrit nouns and verbal derivatives are built on exactly that alternation. The vowel is common in Middle Indo-Aryan as well, since several older combinations resolved into it as the language changed.