Tha ث

Tha is the fourth letter of the modern Arabic order and the shared bowl skeleton carrying three dots above, the only Arabic letter pointed with three. It joins on both sides and reduces to a tooth with its three dots at the beginning and in the middle of a word. Its sound is the voiceless dental fricative heard at the start of the English word thin, a sound Arabic preserved where several of its sister languages lost it, and one that many spoken Arabic dialects have since merged with t or with s.

Tha is a sun letter, so the lam of the definite article assimilates to it in speech although it is still written.

The letter is one of six that Arabic added to the twenty-two letter sequence it inherited from the Northwest Semitic scripts, and its position records that history plainly. In the modern order, which arranges the letters by shape, tha sits next to the ba and ta it resembles. In the older abjad order it is not in the body of the list at all but among the six letters appended at its end, where it carries the numeral value five hundred. Because the inherited names came with the inherited letters, tha has no Northwest Semitic name behind it, no cognate letter in Hebrew or Syriac to which its name can be traced, and no reconstructed pictographic sense of the kind offered for aleph or beth.

The Semitic alphabet that Arabic inherited had twenty-two letters. Arabic has twenty-eight, because the language kept six consonants that the twenty-two letter sequence did not distinguish: tha, kha, dhal, dad, za and ghayn. These six are known in the grammatical tradition as the rawadif, the followers, and the name is literal. They were not slotted into the sequence beside the letters they resemble; they were added to the end of it.

That decision is still visible in the two orders Arabic uses. The abjad order preserves the inherited sequence, running alif, ba, jim, dal and onward through the twenty-two, and then appends the six added letters after it. It is remembered through a set of eight nonsense words, beginning abjad hawwaz hutti, that give the letters in order and that the abjad takes its name from. The modern hija'i order, by contrast, groups the letters by written shape, so that ba, ta and tha stand together because they share one skeleton, and jim, ha and kha stand together for the same reason. That is the order in which the alphabet is now taught and in which dictionaries and indexes are arranged.

The abjad order survives because it carries the numerals. Each letter has a numerical value fixed by its place in the inherited sequence, from alif at one to ghayn at one thousand, and the six appended letters take the six highest values precisely because they came last. This is the reckoning called hisab al-jummal, used for dates in inscriptions and colophons, for chronograms in poetry, and in the letter speculation of some Sufi and occult writers. Two regional conventions exist, the eastern and the western, and they assign several of the values differently.