Are "Shabbat clothes" simply a social custom, or is there some set of halakhic categories that applies to clothing on Shabbat? The common assumption among Jews outside the "black-hat" world seems to be that Shabbat clothing is an issue of how we dress for shul on Shabbat, and some even seem to assume that it is only an issue for Shabbat morning. Neither assumption appears correct from even a quick examination of the sources.

The gemara assumes in several places that people don nicer clothing for Shabbat than during the week. When Naomi tells Ruth to prepare for her encounter with Boaz by "putting on your dress," the gemara assumes that means her Shabbat dress. When the gemara relates how how various amoraim, rabbis of the time of the gemara, preprared for Shabbat, an essential element was putting on special clothing to greet the Sabbath Queen. The Shulhan Arukh says that one should "try" to have special clothing for Shabbat, a requirement presumably only limited by financial need. Rema includes being dressed in our special clothing before Shabbat as an example of kavod Shabbat. He adds that people should ideally put on their Shabbat clothing immediately after bathing, so that he encourages bathing late in the day, after which it will be feasible to get dressed immediately for Shabbat. The Mishnah Berurah, most relevantly to our original question of whether bigdei Shabbat are a social or halakhic issue, points out that one should wear Shabbat clothing even if all alone, or solely in the presence of non-Jews, highlighting his view that we wear Shabbat clothing out of recognition of the inherent holiness of the day, not as a social statement.

Several other halakhic questions assume that there is a set of clothing known as our bigdei Shabbat, such as the question of which other days a person should, or may, wear such clothing. Yamim Tovim, holidays, are not days to wear our Shabbat clothing, since the gemara believes our Yom Tov clothing should be even finer than our Shabbat clothing. Days that are not quite holidays— Hol haMoed, for example, or Purim— are more of a question, and many authorities believe that we should wear our Shabbat finery. On the reverse side, there was serious consideration of whether it was acceptable to wear Shabbat clothing on Shabbat Hazon, the Shabbat before Tisha B’Av, and during the Shabbat of shiva, the Shabbat during the week of mourning for a close relative.

Adjusting our view of Shabbat clothing means that we need to reexamine two subissues, dress code and timing. In terms of dress code, while there is obviously room for social and cultural differences, we can categorically state that Shabbat clothing is supposed to be finer than our weekday clothing. For laborers (or people in computers) who can wear jeans or dirty work clothing all week, even clothing that most people would consider casual, if clean, easily beat out those people’s weekday attire in cleanliness and formality. For those who wear a suit all week, a different standard would apply. There may also be a social element—if a person with a job that allows highly informal clothing lives in a community with professionals, that person should quite possibly wear a suit, to adjust to the community standards of bigdei Shabbat. Recognizing that the day itself demands Shabbat clothing also suggests that we cannot change into non-Shabbat clothing in the afternoon (or on Friday night if we are not attending davening). Other than when we are sleeping, it would seem that any time we are dressed over the course of Shabbat, we should be wearing attire appropriate to the day. In fact, the Shelah explains that we generally say kiddush levana on Motsaei Shabbat because we are wearing better clothing than ordinarily.