(This should not be relied upon for practical halacha. When a question arises a Rabbi should be consulted.)
[The following is a translation from the authors hebrew work Umekareiv Biyamin.]
1. The source for the requirement for a man to cover his head can be found in the Gemara Kiddushin (31a). The Gemara says that Rav Huna (the son of Rav Yehoshua) would not walk four Amos with his head uncovered, because the Divine Presence is above. Similarly, the Gemara in Shabbos (118 b) relates that Rav Huna said, “I will receive (reward- Rashi) for not going four Amos with my head exposed.”
2. Many authorities, including the Tashbetz (559), Bach (O.C. 2), Gra (O.C. 8), Chida (Birkei Yosef O.C. 2), and Maharshal (72), deduce from the above Gemara that one is not obligated to wear a yarmulka, rather it is a Minhag (custom). For if it were an obligation why would Rav Huna expect to receive reward for fulfilling his obligation. Rather, it is not obligatory and Rav Huna was going above and beyond the letter of the law. It is for this reason that Rav Huna expected reward for his actions.
3. It is unclear as to the view of Harav Yosef Karo zt”l regarding whether the head covering is obligatory or customary. In Beis Yosef (O.C. 91) he cites the view of the Tashbetz that it is customary. While in Beis Yosef (O.C. 8) seems to explicitly imply that one is forbidden to walk without a head covering. What’s more, in his Shulchan Aruch, Harav Karo zt”l writes, “It is forbidden to walk in an erect posture. And a man should not walk four Amos with an uncovered head.” The Magen Avraham points out that from the fact that the Shulchan Aruch uses the term “forbidden” regarding walking with an erect posture and not walking without a head covering, it seems that the Shulchan Aruch feels that it is not obligatory. The Chida noticed the discrepancies and cites the Ben Ish Chai that any time one finds a contradiction between the Beis Yosef and Shulchan Aruch we follow the Shulchan Aruch.
The Chida summarizes his view with the following statement, “It is clear from the words of the Gemara and the poskim that it is not forbidden (to walk without a head covering), rather, it is a Midas Chassidus (pious conduct) or praiseworthy to cover one’s head. I, therefore, do not understand the view of Rav Yehuda Ayas zt”l who maintained that it is forbidden to travel without a head covering. Since according to the Gemara and poskim it seems that it is merely customary etc.” (Machazik Bracha O.C. 2)
4. However, the Taz (8:2) suggests that although a headcovering was originally an act of piety, it gained the status of Torah Law, due to the custom of non-Jews to remove their caps as a sign of honor. Since the Torah prohibits Jews from “going in the ways of non-Jews,” one who does not cover his head would therefore be in transgression of a negative Commandment of the Torah. However, Harav Moshe Feinstein zt”l (Igros Moshe O.C. 4:2) questioned this stringent view. He explains that not every action that non-Jews perform is forbidden. It is only forbidden if they do something for religious purposes, promiscuity reasons, or an action that has no clear reason. If they, however, perform an act for valid reasons a Jew is also allowed to act accordingly. For example, a non-Jewish doctor wears “scrubs” to indicate to others that he is a doctor and in case of need he may help. Since there is a rationale for wearing “scrubs” a Jewish doctor may likewise wear “scrubs.” Therefore, argues Harav Feinstein zt”l there is a clear rationale for the actions of non-Jews. They are not covering their head for comfort reasons. It is also not a religious act since many non religious non-Jews do not cover their hair as well. Therefore the view of the Taz is no longer applicable.
[Rav Moshe (Igros Moshe 4:40:14) does admit that there is one case where the view of the Taz still applies, and that is praying without a head covering. Because the non-Jews remove their head covering when praying, one may not pray without a head covering.]
5. It must be noted that although most authorities feel that one is not obligated to wear a yarmulka, it has become a widespread custom amongst Klal Yisroel and one must always adhere to this custom. The Baal Hatanya (2:6) added that since it is customary for a man to cover his head if he fails to do so it is a lack of Tzniyus (which requires us to cover all body parts that are customarily covered). Harav Ovadia Yosef zt”l (Yabia Omer 9:1) noted that wearing a yarmulka nowadays serves as a symbol of one’s affiliation with the observant Jewish community and failing to do so would lead others to believe that he is non-observant. And the halacha of Maris Ayin tells us that we are not allowed to portray ourselves as less observant than we actually are.
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