Siddham Ai 𑖋

Ai is a diphthong, always long, and the second of the two grades by which the grammarians describe the strengthening of i. Where e is the first step, ai is the second, so the three sounds i, e and ai stand as one series produced by a single operation applied once and then again, rather than as three unrelated vowels that happen to sit near each other in the table.

That gives the letter a job in the vocabulary out of proportion to how ordinary it looks. The second grade is what Sanskrit uses to make a word mean something belonging to, descended from, or derived from its base, so a large family of adjectives and abstract nouns is formed by raising the first vowel of a word to this grade. The names of doctrines, schools and lineages are full of them, which is why a letter that looks peripheral in the table is not peripheral on a page of Buddhist philosophy.

Like the three other long vowels that close the vowel series it has no short partner, and none is expected. In metre it is always heavy. Its independent form appears only at the start of a word, and after a consonant it is written as a mark, which is the same arrangement every vowel in the script follows.

The independent form is uncommon, since relatively few words open on the diphthong, and a reader is more likely to meet the letter as a mark attached to a consonant than as a character standing on its own. That is true of most of the vowels after the first two, and it is why the independent series is easier to learn from a chart than from a text.

Sanskrit builds a great deal of its vocabulary by raising a vowel through two fixed steps, which the grammarians call guna and vrddhi. The basic vowels i, u and the vocalic r each have a first grade and a second: i gives e and then ai, u gives o and then au, and the vocalic r gives ar and then ar with a long vowel. The system is regular enough that a reader who knows it can often see the underlying root inside a form that no longer shows it.

The letter table records this without saying so. The four vowels that close the vowel series, e, ai, o and au, are exactly the products of the operation, which is why they have no short partners and why they sit together at the end. Their arrangement is not a list of leftovers but two matched pairs, each pair being one vowel taken up two steps.

The point matters for reading Siddham because it makes the script partly predictable. Buddhist Sanskrit generates terms constantly by this route, and the second grade in particular marks the words that name a school, a doctrine, a class of being or a quality abstracted from something concrete. A reader who recognises the vowel at the front of a word already knows a good deal about what kind of word it is, before working out what its root means.