Gematria and Isopsephy
In a few systems of alphabetic writing, scribes used the same symbols for sounds as they did for numerals. In other words, they didn’t have distinct symbols for numbers from their alphabet; where English speakers have the letters A through Z and the numerals 0 through 9, other languages might use the same character to represent 4 as they would the sound for “D”. Thus, a string of characters might be read either as a word or as a number, depending on the context. Most of the world uses distinct numerals nowadays due to influence from modern technology and science, but this wasn’t always the case.
The practice of ascribing numerical values to words by interpreting the characters as numbers instead of sounds is old, and is called gematria in Hebrew or isopsephy in Greek. Words, phrases, or names that had the same numerical value were thought of to be the same or have the same essence on a different level. Although we normally refer to this as numerology in English, this is an inappropriate generalization of this kind of study, since numerology also studies the general occult properties of numbers and their correspondences.
Hebrew gematria (from Greek γεωμετρία, “geometry”) relies on the Hebrew script, which has 22 letters, plus another five which are distinct final forms of several of the letters, yielding 27 letters total. Each of the letters is assigned a value corresponding to a multiple of 1 through 9, as below.
Here, the first nine letters are given the values 1 through 9, the next nine given the values 10 through 90, and the last nine given values 100 through 900. The last five letters are final forms of the letters kaph, mem, nun, peh, and tzaddi. This is only one of many schemes used to assign numerals to the Hebrew letters, but this is the most common. So, given this scheme, the word for Mercury in Hebrew, Kokab כוכב, is assigned the value 48.
K + V + K + B
20 + 6 + 20 + 2
In another example, the word for wine, yayin יין, and secret, sod סוד, both have the same value of 70 (50 + 10 + 10 and 60 + 6 + 4). Thus, because they’re numerically the same, they have the same effect or essence when compared or conceived of on another plane of existence. In Hebrew culture, gifts are sometimes given in multiples of 18, the value of the Hebrew word for “life”.
Greek isopsephy (ἴσοψῆφία, literally “same pebble”, as in the same idea of Latin calculus, “little stone”) is another system similar to Hebrew gematria when applied to the Greek alphabet. The Greek alphabet, having come from the same origin as the Hebrew alphabet, also used letters as numerals, and likely did so earlier than Hebrew. A big difference is the number of characters: Hebrew has 22 letters with 5 extra, adding to 27, while Greek has 24. To make up for the lost characters, Greek used three obsolete letters for the sole purpose of transcribing numbers: digamma (Ϝ) for 6, qopppa (Ϙ) for 90, and sampi (ϡ) for 900. Digamma was a “w” sound, qoppa a uvular “k” sound like Hebrew qoph, and sampi was probably a lengthened “s” or “ks” sound.
Although not used to quite the same extent as gematria, isopsephy can still be seen in some religious or graffitic examples. Consider that infamous Number of the Beast, 666: in the original verse, it says that the wise man may count the Beast’s number, but “count” is rendered with a word with the same “pebble” root as isopsephy. The Greek alphabet comes into better use in astrology since, with 24 letters not counting the obsolete ones, it matches up well with divisors and multiples of 360.
As for English or languages that use the Roman script, well, I can’t say much about it. Unlike Greek or Hebrew, Latin (the original language of the Roman script) never used its letters for counting, and has added and removed several letters across the course of its lifetime that never really matched up in a good way with the schemes given above. Agrippa tried to fix this by creating two new values “Hu” and “Hi”, with “Hu” becoming “W”, but “Hi” was never really used, and so this system fell apart. Aleister Crowley developed a scheme that assigned the 26 letters the values 1 through 26, but this spawned other attributions and different orderings of the values to letters. While I don’t discount a usable Roman gematria, I haven’t seen a convincing example of it being used for a language other than Greek or Hebrew.