Siman 395

It is a decided law in Pesachim (Pesachim 4a) that part of the day is like the whole of it regarding mourning. And it is not specifically regarding mourning, for in many matters we say part of the day is like the whole of it: regarding taking root, and regarding nezirut, and in every place part of the day is like the whole of it (Rashi Niddah 33a). Therefore, whether in the laws of seven or in the laws of thirty, part of the day is like the whole of it. And even regarding the matters that we permitted from the third day and onwards – we say on the third day part of the day is like the whole of it, as I wrote in siman 393 section 8, see there. (And I saw one who wrote that regarding three we do not say part of the day is like the whole of it. And this is against the words of the Shulchan Aruch there.)

And ostensibly, since a part of the day is like the whole of it, if so, even a part of the night should suffice regarding the matter of thirty. For when a part of the night belonging to the thirtieth day has passed, the decree of thirty should be nullified for him. For granted, regarding seven it is impossible for it to be so, as we require that the comforters stand up from beside him (Moed Katan 22a) and as I wrote in siman 375, and the comforters come by day and not by night. But regarding the matter of thirty, why should a part of the night not be considered like a part? And indeed, this is the opinion of the Ramban and the Rosh in the name of the Ram (see Beit Yosef). However, the opinion of the Rashbam and the Rivam is that at night the matter is not evident, and we require a part of the day (see there). And it is not because according to the essential law it is so, but rather that such is the custom of the world. And so our teachers, the authors of the Shulchan Aruch, left it unspecified. And we find regarding one who keeps a day for a day that guarding at night is not considered guarding. However, regarding the matter of a distant report—even a part of the night suffices. Therefore, one who heard a distant report at night, since one hour is sufficient—it is discharged even at night.

And according to this, when a deceased relative died and was buried on the first day, such that the days of his mourning are completed on Shabbat – he is forbidden on Friday night in matters of privacy and in all matters forbidden to a mourner on Shabbat until the morning after the prayer. And this appears to be a simple matter, for when we say on the seventh day "part of the day is like the whole of it," it is permitted even in tashmish after part of the day. However, there are those who are concerned regarding this. (See Turei Zahav, Orach Chaim, the end of siman 555, where from the poskim it appears that it is permitted. But in Sefer Chasidim and likewise in a responsum of Maharam of Rothenburg, they forbid tashmish until the night, see there. And it is a wonder that he cited responsum 549, and I examined it there and it is explicitly the opposite, that for all matters part of the day is like the whole of it, see there. And it requires further study.)

Therefore, since the comforters have stood up from beside the mourner on the seventh day – he is permitted in all matters that were forbidden to him during the seven, for a part of the day is like the whole of it. It makes no difference whether it is a part of the seventh day or a part of the thirtieth day. And on the thirtieth day he is permitted from the rising of the sun, for on the thirtieth day there are no comforters. And once the sun rises – the decree of the thirty is nullified for him. Our teacher, the Rema, wrote that in these lands where the comforters are not accustomed to come on the seventh day – one must wait until the time they are accustomed to come on other days, which is after the departure from the synagogue, for then the comforters are accustomed to come. And it is not as some are accustomed to wait one hour of the day, for the matter depends only on the standing up of the comforters. Thus far his words. And such is the widespread custom and it is not to be changed.

One whose father or mother died on Rosh Chodesh Nisan, we do not say on the twenty-ninth of Adar "a part of the day is like the whole of it." For specifically regarding matters that depend on days is "a part of the day is like the whole of it" applicable, and not regarding that which depends on months, for if not so, let us also say "a part of the month is like the whole of it." Rather, he must observe the matters forbidden during the twelve months until Rosh Chodesh Nisan enters. Our teacher, the Rema, wrote that they are accustomed to add to it further the day on which the father or mother died, to observe therein the law of twelve months, and it is correct. Thus far his words. And this is according to his approach in siman 391 that yahrtzeit is like mourning. However, according to what has been explained there, it is not so; see there in section 14. Yet according to those who say that in the first year one should be concerned—certainly he should observe so. And it appears to me that if his twelve months concluded on a Rosh Chodesh that is two days of Rosh Chodesh—he does not need to observe his mourning except until the first day. And even though according to the count of the days of the month it belongs to the past month, nevertheless, since it is Rosh Chodesh—one should not be stringent in this.