Certain activities – such as building, tying, weaving, writing, dyeing and sewing – are not prohibited on Shabbat unless they are made to last. For example, one may tie a knot that is not tied in a professional manner and will be untied within seven days, such as shoelaces or the ribbon around the Torah scroll, on Shabbat afternoon. So too a safety pin may be used on Shabbat since it is not a form of permanent sewing. Similarly, writing or painting with fluid that fades away, or writing on a substance that does not retain script, is not a melachah in the Torah sense of the term (melachah de’oreita), though it is rabbinically prohibited (melachah derabbanan).
When do the above activities become permanent and, therefore, a melachah de’oreita? According to the Rambam, if the product lasts throughout Shabbat it is a melachah de’oreita. According to Rashi, however, it must have the ability to last forever.
May one build a structure on Shabbat if one intends to take it apart on Shabbat shortly after its use? This question is debated between two sages in the Jerusalem Talmud. Rabbi Yosi Bar Nun maintains that it is prohibited because the Mishkan itself, from which we derive the 39 melachot, was a temporary structure. Rabbi Yosah disagrees. He maintains that it is permitted because in his view the Mishkan was, in the eyes of the people, a permanent structure. They never knew when God would require them to move on and until such time they lived their lives in a state of permanence.
Whereas the Jerusalem Talmud rules in accordance with the first view, the Babylonian Talmud rules in accordance with the second and maintains that this type of structure is not considered a melachah at all. The debate is picked up by Rishonim and Acharonim in connection with the construction of a provisional tent on Shabbat. According to the Rif, this is a melachah de’oreita. According to the Rambam, it is a melachah derabbanan. And according to Rashi and the Rosh, constructing a provisional tent is permissible in the first place.
Based on the above authorities who prohibit the construction of a provisional tent on Shabbat, the Noda Beyehudah considered the opening of an umbrella on Shabbat a melachah de’oreita and prohibited its use in his community, even if opened before Shabbat, because onlookers would think it was opened on Shabbat (marit ayin).
Conversely, basing himself on the authorities who permit the construction of a provisional tent on Shabbat, the Chatam Sofer maintains that using an umbrella on Shabbat is not even a melachah derabbanan and he did not object to it in his community in the presence of an eruv.
The consensus of opinion among today’s poskim prohibits the use of an umbrella on Shabbat even in the presence of an eruv. The Chofetz Chaim prohibits it because, irrespective of its temporary nature, it is intended to be used as a tent for protection against the elements. The Chazon Ish prohibits it because it makes Shabbat look like a working day. Rav Ovadia Yosef, after summarizing all the authorities for and against, sides with the authorities who prohibit it.