Abjad

Hisab al-jummal, the reckoning of the total, assigns each of the twenty eight letters of the Arabic alphabet a fixed numeric value and sums a word's letters to find its total, the same basic operation Hebrew gematria and Greek isopsephy perform on their own alphabets. Two distinct orderings of the values survive and remain in use in different regions. The standard Eastern or Mashriqi order follows the historic sequence of the Northwest Semitic abjad that Hebrew, Aramaic and Arabic all ultimately share, running alif through ghayn in a pattern that mirrors the old Phoenician letter order rather than the alphabetical order taught for reading and writing today.

A separate Western or Maghribi order, historically used in North Africa and in Islamic Spain, rearranges several of the later letters differently, so the same word can sum to two different totals depending on which regional convention is applied, a genuine and documented variation rather than an error in either system. Because the abjad numerals also served as an alternative to Hindu-Arabic numerals for ordinary counting and dating for centuries, mastering the value table was practical knowledge for scribes and astronomers as much as it was an esoteric skill.

One of the abjad system's most distinctive uses is the chronogram, a phrase or line of verse composed so that the sum of its letter values equals a particular year, most often the year of a building's completion, a ruler's accession or a notable death. Composing a chronogram that reads sensibly as a sentence while also summing to the correct date was a genuine literary art across the Persianate and Arabic speaking worlds, and inscriptions built this way still appear over gateways and on tombstones from Ottoman Istanbul to Mughal India.

Abjad numerals also underlie ilm al-huruf, the science of letters, a current within Islamic esoteric thought that treated the Arabic alphabet, its numeric values and the combinatorial possibilities between letters as a key to hidden properties of language, nature and the divine names, a strand of speculation connected to the wider tradition of Arabic occult science that also produced influential work on alchemy and natural magic. As with the comparable Jewish and Greek letter-number traditions, the arithmetic itself is straightforward and well documented; the interpretive claims built on top of it, about what any particular total is supposed to mean, belong to the specific school or author who advanced them rather than to a single unified doctrine.