Origin of exemption on covering hair for unmarried women

Question

I've studied tons of various Poskim and websites discussing aspects of covering hair for women so I am familiar with the practical Halachot.

If I'm right, the default state is that all women (married and not, young and not) are obligated to cover their hair (as שער באשה ערוה - Brochos 24a, see Shu"A EH 21:2) but unmarried are Rabbinically exempt and allowed not to (I'm aware that some argue):

"לא תלכנה בנות ישראל פרועות ראש בשוק אחת פנויה ואחת אשת איש:"
Jewish women may not go with uncovered head in the marketplace, whether married or not."

Practically ALL the Poskim agree on the fact that בתולות are not obligated but I failed to trace it to the original source. Please help me find one - where did it start?

Answer 1

I commend your question in explicitly stating your assumptions, such that the question follows.

One of your assumptions is that

the default state is that all women (married and not, young and not) are obligated to cover their hair (as שער באשה ערוה - Brochos 24a, ...)

(The ellipses are my own; because I only wish to discuss the gemara in Berachot, rather than the Shulchan Aruch's understanding of a different gemara.) The question is whether the words באשה in the gemara you mentioned refers to all women, married or not, and young or not.

It is not obvious because the word אשה in Hebrew sometimes refers to a woman, and sometimes it refers to a wife (an אשת איש). If in this gemara it refers specifically to a married woman, then this particular assumption upon which your question rests does not hold.

If we look at Rashi in the context of this gemara, he writes about shok be'isha erva:

שוק - באשת איש: ערוה - להסתכל וכן באשתו לק"ש:

He writes that it applies to a married woman specifically. It stands to reason that this definition of specifically eshet ish also applies for the next statement in the gemara as well.

In terms of your assumption on the second source, that Ketubot 72 (which you should cite rather than Shulchan Aruch's interpretation of it), which speaks to bnot Yisrael, it is a question of balancing ambiguous sources. The context of the gemara in Ketubot speaks of women leaving marriage without their ketubah, so is explicitly married women. The Tanna deVei Rabbi Yishmael finds (as the other answer notes) this warning to women from the context of Sotah, so even though employs the term bnot Yisrael, the context might mean Jewish daughters in the sense of married Jewish daughters. It does not explicitly say non-married Jewish daughters.

Then, as the Chelkas Mekokek points out, there are other sources such as an explicit Mishna in the second perek of Ketubot that יוצאה בהינומא וראשה פרועה is evidence that she was a virgin. As a result, this idea that unmarried women must cover is only to non-virgins. That is one way of harmonizing and balancing the competing and ultimately ambiguous sources.

Answer 2

I believe your understanding of שער באשה ערווה is incorrect. That gemarra is discussing a man's obligation to avoid reciting words of Torah when uncovered hair is in his sight. It creates no obligation for a woman to cover her hair. For example, let's say a married couple are alone in a place where she is allowed to have her hair uncovered. Is her hair erva? Yes. Can he recite shema while looking at her? No. Must she cover it? It is after all, erva. The answer is still no.

What is the source for a woman to cover her hair? From the Sotah ritual. That's describing a married woman. The default position is no one has to cover their hair. Why would the opposite be true? The Torah teaches us that a married woman must cover her hair. If the Torah doesn't speak about an unmarried woman, we're still at the default understanding. The burden of proof is on the one who says otherwise. This is why no one discusses the "source", as there is none.