1) USING THE LIGHT OF A CANDLE KINDLED BY A NOCHRI ON SHABBOS
QUESTION: The Mishnah lists three cases in which a Jew may benefit from a Melachah performed by a Nochri on Shabbos: (a) If a Nochri lights a candle on Shabbos, a Jew may use the light. (b) If a Nochri draws water to feed to his animal, a Jew may use that water "after him" for his own animal. (c) If a Nochri builds a ramp from a boat to the shore, a Jew may use that ramp "after him."
Rashi explains that the Jew may use the water or ramp only after the Nochri has used it, because he must make it apparent that the Nochri drew the water or built the ramp for himself and not for the Jew. Why, then, does the Mishnah not say that the Jew may use the light only "after him" in the first case, in which a Nochri lights a candle on Shabbos from which a Jew may benefit?
ANSWER: RAV ELAZAR MOSHE HA'LEVI HOROWITZ explains that when it comes to a light, by nature a person normally derives benefit from it at the moment that he lights it, because it is in front of him and it provides him with light. It was not necessary to say that the Jew uses it after the Nochri uses it, because at the moment that the Nochri lights it, he has already used it.
2) HALACHAH: BENEFIT FROM MELACHAH PERFORMED BY A NOCHRI
The Gemara discusses when a Jew may benefit from a Melachah performed by a Nochri on Shabbos. The Gemara concludes that there are two types of cases, each with its respective Halachos. The first type of case is one in which a majority of the people in that place (who might benefit from the Melachah that was performed) are not Jewish. The second type of case is one in which a majority of the people in that place are Jewish, or the numbers of Jews and Nochrim are equal.
(a) Where most of the people are not Jewish, a Jew may benefit from Melachah performed by a Nochri if any one of the following three conditions is fulfilled:
1. The Nochri does not know who the Jew is.
2. It is the type of Melachah that serves many people the same way it serves one person ("Ner l'Echad, Ner l'Me'ah").
3. The Nochri performed the Melachah while the Jew was not present.
RASHI adds that the Nochri must actually benefit from the Melachah first before the Jew may benefit from it.
(b) Where most of the people are Jewish, or the numbers of Jews and Nochrim are equal, a Jew is permitted to benefit from the Melachah performed by a Nochri only when it is clear that the Nochri performed the Melachah for his own use.