Tzadi is the eighteenth letter and its value is ninety. Like mem, nun, peh and kaf, it has a final form: bent at the beginning and in the middle of a word, it becomes straight at the end and descends below the line. The Talmud reports that these final forms, "the Seers said them," then specifies that they already existed: it had been forgotten which goes in the middle and which at the end, and the Seers restored the rule, "open in the middle of a word, closed at the end."
In Sefer Yetzirah, tzadi is one of the twelve simple letters, placed at the twelve diagonal edges of space, "the arms of the world," with twelve foundations, from sight to sleep. For tzadi the book writes: "He made the letter tzadi king, He bound a crown to it," and formed through it the Bucket in the world, the month of Shevat in the year and the stomach, kivah, in the soul. In the classification of sounds, tzadi belongs to the letters of the teeth, zayin, samekh, shin, reish, tzadi.
The Talmud reports the reading of the alphabet that children once gave in the study hall, which the Sages came to relate to Rabbi Yehoshua ben Levi. For tzadi they said: "bent tzadi, straight tzadi: a righteous one bent, a righteous one straight." The Gemara objects: that is the same as for the nun, "a faithful one bent, a faithful one straight." It answers: Scripture added a bending to his bending; "from here, the Torah was given with bowed head." One understands that the righteous one, bent in humility, will one day stand upright, and that the Torah is received with a double humility.
The Alphabet of Rabbi Akiva gives two texts. In the account of the letters presenting themselves before the Holy One, blessed be He, before creation, tzadi pleads: through me they will say every day "Your righteousness," tzidkatekha, "Your righteousness is like the mighty mountains," and "the L-rd is righteous, He loves righteousness." The answer is no: through you many troubles, tzarot, will come upon Israel, as it is written "it is a time of trouble for Jacob." In the other version, Rabbi Akiva reads: "do not read tzadi, but tzedek," the righteousness of the Holy One, blessed be He, toward human beings: the knowledge, wisdom, understanding, opening of the mouth and answer of the tongue He gives them, by which the whole world endures.
The sources read in tzadi the righteous one and righteousness, and each time humility. The bent righteous one of the Talmud and the righteousness given in words and wisdom in Rabbi Akiva meet: whatever is righteous in a person comes from above, and it is with bowed head that one receives it.
