The obligation for a married woman to cover her hair when she leaves the house is based on a Mishnah in Ketuvoth (72a):
Mishnah. "These are to be divorced without receiving their kethubah: a wife who transgresses the law of Moses or [one who transgresses] the practice of Jewish women. And what is [regarded as a wife's transgression against] the law of Moses? Feeding her husband with untithed food, having intercourse with him during the period of her menstruation, not setting apart her dough offering, or making vows and not fulfilling them. And what [is deemed to be a wife's transgression against] the practice of Jewish women? Going out with her head uncovered, spinning in the street or conversing with every man." Translation: Rabbi Dov Linzer. For those who wish to read in Hebrew:
מתני'. ואלו יוצאות שלא בכתובה: העוברת על דת משה ויהודית. ואיזו היא דת משה? מאכילתו שאינו מעושר, ומשמשתו נדה, ולא קוצה לה חלה, ונודרת ואינה מקיימת. ואיזוהי דת יהודית? יוצאה וראשה פרוע
Now I wish to point out two things. First a very literal read of the Mishnah, seems to imply that the obligation to cover hair begins when a woman leaves her home. ''Going out...." states the Mishnah. But more on this later... Second, the Hebrew for 'Law of Moses' is Dat Moshe while the Hebrew for 'the practice of Jewish women' is 'Dat Yehudit.' Now, the latter raises all kind of questions regarding how Dat Yehudit ought to be defined--Do Jewish women decide for themselves? Do the social mores of a host country or culture play a role? Is it based on what men find to be provocative? Is it rabbinic? Is it biblical?
The discussion starts in the Talmud, continues with the Rishonim, and has not ceased till this day. But I thought to point out something that is of far more academic interest, conceding that it probably has limited application in terms of the halachic process. Nevertheless, I offer two pieces of evidence that Dat Yehudit was not the original expression. The first is from an early Mishnah manuscript held in the Biblioteca Palatina. For those who can make out the Hebrew, it's in the bottom left-hand corner of the following Link. The Second is from a manuscript of the Mishnah Ketubot, held in a Library in Budapest. The Mishnah (7:6) is found on the right column.
Well, what both these manuscripts state plainly is that the original expression is not Dat Yehudit (Practice of a Jewish Woman) but Dat Yehudim (Practice of Jews). What difference does this make? Perhaps none whatsoever, especially since all the Talmudic manuscripts that I found use Dat Yehudit in their discussions. (Vatican EBR 113; Vatican EBR 130; Vatican EBR 487.11; Cf. Dikdukei Sofrim HaShalem: Ketuboth** for Genizot)
But to my mind at least, the parallel of Dat Moshe and Dat Yehudim--the Practice of Moses and the Practice of Jews, reaffirms a division between the Laws of the Jewish People and the Customs of the Jewish People. The latter naturally being far more fluid than the former. I admit, however, that even this might not always hold true, the force of custom is often stronger than that of law, and besides, we Jews are pretty stubborn.
To be continued next week...