According to the secular, Socialist affiliated Jewish Daily Forward, its use as an amulet is very recent, originating in stories from 18th century Eastern Europe first used in amulets from the mid 20th century.
Chai as a symbol goes back to medeival Spain at the latest. Letters as symbols in Jewish culture go back to the earliest Jewish roots, the Talmud states that the world was created from Hebrew letters which form verses of the Torah. In medieval Kabballah; Chai is the lowest (closest to the physical plane) emanation of God. According to 16th Century Greek rabbi Shelomo Hacohen Soloniki; in his commentary on the Zohar, Chai as a symbol has its linkage in the Kabalah texts to God's attribute of 'Ratzon', or motivation, will, muse. The Jewish commentaries give an especially long treatment to certain verses in the Torah with the word as their central theme. 3 examples are Leviticus 18 וָחַי בָּהֶם 'Chai Bahem', 'and you shall live by [this faith]' (as opposed to just doing it), this is part of the section dealing with the legacy of Moses Our Teacher following his death. Deuteronomy 31:9 " רְאֵה נָתַתִּי לְפָנֶיךָ הַיּוֹם, אֶת-הַחַיִּים וְאֶת-הַטּוֹב, וְאֶת-הַמָּוֶת, וְאֶת-הָרָע. 15 "Verily, I have set before thee this day life and good, and death and evil,in that I command thee this day to love the LORD thy God, to walk in His ways, and to keep His commandments and His statutes and His ordinances; then thou shalt live." There is nigh an ancient Jewish commentator who does not comment on that verse. The Shema prayer as well speaks of the importance of Chai, to live and walk in the Jewish cultural lifestyle.
Two common Jewish names used since Talmudic times, are based on this symbol, Chaya feminine, Chayim masculine. The Jewish toast (on alcoholic beverages such as wine) is l'chaim, 'to life'.
The word is made up of two letters of the Hebrew alphabet - Chet (ח) and Yod (י), forming the word "chai," meaning "alive," or "living." The most common spelling is "Chai", but the word is occasionally also spelled "Hai". The usual modern pronunciation of this word is [χai̯], while a transcription of the Biblical and Mishnaic pronunciation would have likely been [ħai̯] (with a pharyngeal consonant).
There have been various mystical numerological speculations about the fact that, according to the system of gematria, the letters of chai add up to 18 (see "Lamedvavniks" etc.). For this reason, 18 is a spiritual number in Judaism, and many Jews give gifts of money in multiples of 18 as a result.
In Jewish culture
In Hebrew, the related word chaya means "living thing" or "animal", and is derived from the Hebrew word chai (חי), meaning "life".
Jews often give gifts and donations in multiples of 18, which is called "giving chai". Mailings from Jewish charities usually suggest the amounts to give in multiples of chai (18, 36, 54, dollars, etc.) rather than the usual multiples of 25.
It appears in the slogan "ʿam yisraʾel ḥay!" (עַם יִשְרָאֵל חַי, "The people of Israel lives!").
It is heard in a BBC recording from April 20, 1945 of Jewish survivors of the Bergen-Belsen concentration camp five days after their liberation. This was the first Sabbath ceremony openly conducted on German soil since the beginning of the war, with people still dying around them, singing what would become the Israeli national anthem, Hatikvah. At the end of Hatikvah, British Army Chaplain Leslie Hardman shouts out, "Am Yisrael Chai, The children of Israel still liveth!" 
In the Eurovision Song Contest 1983, which was held in Germany four decades after Shoah, Israel was represented with a song called Chai performed by Ofra Haza which included the line Am Yisra'el chai.
In Johannesburg (South Africa), there is an English language Jewish radio station called Chai FM.
- Exploring 'Chai' Culture, Jewish Daily Forward, 2012
- Sheat Ratzon al ha-Zohar 35
- Aish: Am Yisrael Chai -- The Eternal Nation: (MP3 file) - A vocal recording by Jewish singer, Sam Glaser of the traditional Jewish song]
- Nana.co.il, original Site with Newspaper Article (Hebrew)
- "Elvis' Jewish Heritage", Elvis Presley News, 2007. Retrieved February 10, 2008. Note photograph of Elvis performing with Chai necklace toward the bottom of the page.
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