In the Twilight: Melacha During Bein Hashmashos

I realized right after shkiah that the dining room lights are off. May I ask a non-Jew to turn them on?

Bein hashmashos, the twilight between shkiah and tzeis, may already be night (see issue 601). Melacha is therefore forbidden mide’oraisa, and derabanan prohibitions apply as well. Being unsure whether bein hashmashos has begun is not a sfek sfeika (double doubt), since a doubt that stems only from one’s own lack of information is no doubt.¹

Yet Chazal did not extend their decrees (shvusim) to bein hashmashos where there is a mitzvah or where a person has an urgent need.² The Alter Rebbe lists the needs that qualify: a genuine Shabbos need one cannot easily do without, even if it is not a great need; a great need, where one would otherwise suffer real distress; or a substantial loss (hefsed merubah).³

Asking a non-Jew to do a melacha is forbidden only miderabanan (see issue 887). For a mitzvah or a great need, one may therefore ask him during bein hashmashos to do even a full melacha. The Alter Rebbe thus rules that one may ask a non-Jew to light a lamp for Shabbos then, since that is a mitzvah need.⁴ Turning on the lights for the Shabbos meal is the same. (For other examples, see issue 604.)

A Jew doing a shevus himself, however, has a firm limit. A shevus that could easily lead to an issur de’oraisa was not relaxed during bein hashmashos, even for a mitzvah. Moving muktza is permitted in the above situations, but carrying in a reshus harabim less than four amos at a time is not, since it could easily lead to carrying four amos at once. The same applies to carrying out in an unusual manner (kilachar yad), or by one person lifting an item and another setting it down.⁵ Some forbid having a non-Jew cook during bein hashmashos, lest the Jew end up taking part in the cooking; others are not concerned.⁶

Davening Maariv changes this. Once a person has davened Maariv of Shabbos or answered borchu, or most of his congregation has answered borchu even without him, he may no longer do any shevus himself, even for a mitzvah, though he may still ask a non-Jew to do a melacha for a mitzvah or a great need.⁷ (The Mishnah Berurah holds that this applies already from when the congregation says Mizmor Shir or Lecha Dodi.⁸) Either way, in a city with many shuls, one congregation is not drawn after another.⁹

What about accepting Shabbos without davening? The Alter Rebbe rules that such an acceptance, even a congregation’s Mizmor Shir, is only tosefes Shabbos. Only accepting the essence of the day (itzumo shel yom) through Maariv forbids shevusim.¹⁰ Tosefes, he explains, is no stricter than bein hashmashos itself, when melacha carries a safek kares, and yet shvusim are permitted.¹¹

See Sources (open PDF)