Arachin, Chapter 2, Mishnah 2. Our chapter is built around a single literary formula: "ein pochatin... velo yeter al...", there are never fewer than this many and never more than that many. The mishnah gathers halachot from completely different corners of Torah and lines them up according to their lower and upper limits. Here we are taught four such limits: the number of full months in a year, the age of the shtei halechem when they are eaten, the age of the lechem hapanim when it is eaten, and the range of days within which a boy receives his brit milah.
The Jewish calendar: why months are not all the same length
The calendar of the nations rests on the sun. A full circuit of the earth around the sun takes about three hundred and sixty five days plus a quarter, and that figure sets the length of the secular year. Ours is a different system, keyed to the moon as it travels around the earth. At the start of each month the moon shows itself as a thin sliver; with every passing night more of it becomes visible, until by mid month its face is complete. From there it wanes, a little less appearing each night, until nothing at all can be seen, and then a new moon opens the next cycle. A Jewish year is made up of twelve such cycles.
The moon completes its orbit in approximately twenty nine and a half days. (We will refine that figure shortly in order to add an important detail, but let us work with twenty nine and a half for the moment.) A Jewish month, however, cannot be built out of half days. A month must be made of whole days, so that the calendar has a settled, complete character to it. The solution is that some months are given twenty nine days and some are given thirty. A thirty day month is called me'ubar, "pregnant," because it carries something extra; a twenty nine day month is called chaser, lacking.
One would assume the obvious arrangement: simply alternate, thirty and twenty nine, thirty and twenty nine, and you arrive neatly at the average of twenty nine and a half. But the lunar cycle is not exactly twenty nine and a half days. It is twenty nine and a half days plus forty four minutes and three and a third seconds. Those extra minutes, multiplied over twelve months, come to more than nine hours in a single year, and once you accumulate that over three years you find yourself needing to add a day, sometimes even two, so that the calendar remains in reasonable alignment.
Fixing the length of each month was the work of the chachamim who sat in the Sanhedrin, and they were not bound by any mechanical rule. Two thirty day months could be declared one after the other, and elsewhere in the very same year two months of twenty nine days might likewise follow each other. Nothing obliges a year to be split evenly into six of each; one year leans toward the full months, another toward the deficient ones. What the halachah does supply is a lower boundary and an upper one.
What lies behind those boundaries? The chachamim wanted the first of Tishrei to arrive at more or less the same time as the moon's renewal. Pile up too many twenty nine day months, nine of them, for instance, and Rosh Hashana would be announced while the new moon was still a good stretch away from becoming visible. Such a result cannot stand. It makes no sense to proclaim the day of a new month when there is as yet no new moon in the sky.
This is precisely the ruling of our mishnah. "Ein pochatin", we never go below, "me'arba'ah chodashim hame'ubarim bashanah", four thirty day months in a single year: that is the lower boundary. "Velo nireh yeter al shemonah", and it is not proper for the tally of full months to climb past eight. Between four and eight, then, the calendar holds steady and the moadim arrive in their appropriate seasons.
The shtei halechem: two days or three
From the calendar the mishnah turns to the shtei halechem, the pair of loaves offered in the Beit Hamikdash on Shavuot. Accompanying them are two lambs brought as a shelamim on behalf of the entire nation. The loaves themselves never go up on the mizbeach. Rather, they undergo tenufah, waving, held together with the two animals. The lambs are then shechted and brought up as a korban, and the kohanim consume their meat together with these two loaves.
Shavuot is the day of their offering, but not the day of their baking, which has to take place earlier. As a result, the kohanim never eat them fresh from the oven on the day they were made. The mishnah supplies the span: "Shtei halechem ne'echalot", the two loaves are consumed, "ein pachot mishnayim", no sooner than two days from the time of their baking, "velo yeter al sheloshah", and no later than three days from then.
How does this work out? When Shavuot falls on an ordinary weekday, the loaves are baked the day before. That is day one, and they are eaten on day two. But when Shavuot falls on a Sunday, the baking cannot be done on Shabbat, so it is pushed back to erev Shabbat, Friday. Count it: Friday, Shabbat, and then they are eaten on Shavuot itself, Sunday, a total of three days. That is the second limit of our mishnah.
The lechem hapanim: nine days or eleven
A second bread follows the identical pattern: the lechem hapanim, the twelve loaves laid out upon the shulchan in the Beit Hamikdash. Every Shabbat brought a fresh set. The previous week's loaves were lifted off the shulchan, the two bowls of levonah that had stood alongside them went up in smoke on the mizbeach, and the kohanim ate the bread. Here too there was no baking on Shabbat, exactly as with the loaves of Shavuot.
Says the mishnah: "Lechem hapanim ne'echal", the showbread is eaten, "ein pachot mitish'ah", not less than nine days from its baking, "velo yeter al echad asar", and not more than eleven. These are the twelve loaves set out upon the shulchan on one Shabbat, left in place through the week, and consumed by the kohanim when the next Shabbat arrives.
How do we arrive at nine? The loaves are baked on Friday, which is day one. On Shabbat, day two, they are arranged on the shulchan, and there they remain for the entire week until the next Shabbat, when they are eaten. Count from the baking and you reach day nine. That is the minimum.
And where does eleven come from? Should yom tov land on Friday, baking is impossible then, so the loaves are prepared on Thursday, the eve of the festival. Counting from that Thursday until the second Shabbat afterward, when they are eaten, gives ten days. Now suppose the two days of Rosh Hashana occupy Thursday and Friday. Baking retreats to Wednesday: Wednesday is one, the two festival days are two and three (three being the Friday), Shabbat is four, when the loaves go onto the shulchan, and there they sit until the Shabbat a week later, when the kohanim eat them. Eleven days, the largest distance the halachah allows between the oven and the kohanim's table.
Milah: the eighth day and the twelfth
The last of the four limits concerns milah. Ordinarily a boy enters the brit on day eight after he is born. Lo aleinu, should the infant be too weak, the milah waits until he is fit. When day eight coincides with Shabbat or with yom tov, the milah goes ahead all the same. However, a milah that was not carried out at its appointed time is never performed on Shabbat or yom tov; it waits for a weekday. Only the milah of day eight itself carries the strength to set Shabbat and yom tov aside. Once the proper day has slipped by, nothing licenses us to override them. What the mishnah now presents is the case of a perfectly healthy infant who may not be circumcised on Shabbat because it is uncertain whether this really is his eighth day, and how long his brit may consequently be postponed.
"Katan nimol", a child is circumcised, "ein pachot mishmonah", never earlier than day eight. A healthy baby, with nothing standing in the way, has his milah on that day, and there is no situation in which it takes place any sooner. "Velo yeter al shenem asar", and the far end of the range is day twelve from birth. For a healthy child, then, the brit falls somewhere between day eight and day twelve.
In the standard case the brit takes place when the boy is eight days old. Difficulty enters with bein hashemashot, the interval separating shkiah, when the sun sets, from tzeit hakochavim, when the stars come out. To which day does that interval belong: the one now ending or the one now beginning? A baby who arrives within it leaves us with a genuine safek, whether his birth occurred while it was still day or already at night, meaning already on the following date.
The practice we follow is to begin the count of eight from the later day, the one that opens with nightfall, so that we can be sure the milah is not performed prematurely. He is then certainly no younger than eight days, even though in truth it may be his ninth. Far more could be said about this subject and its background than we can cover here, but that is the operating rule.
In other words, we do not say, "He was born with five minutes left in the day, so that day counts as day one." Once he is born after sunset, we attach the birth to the day that is coming in, with the result that he may in fact be circumcised on what is truly his ninth day. Better that than to risk a milah on the seventh day, which would be no milah at all.
So much for a bein hashemashot birth on a weekday. Friday evening changes the picture. Take a boy who arrives after shkiah on Friday, in the twilight leading into Shabbat. The Friday a week later cannot serve for his brit, since it may be his eighth day but may equally be only his seventh: if the expiring Friday is left out of the count, then Shabbat is one, Sunday two, Monday three, Tuesday four, Wednesday five, Thursday six, and Friday is merely seven. Friday is therefore ruled out, just as it would be in any weekday case of this kind.
Shabbat is ruled out too. Only where it is beyond doubt that the birth occurred on Shabbat may a boy be circumcised on Shabbat, for the license to override the day rests on the certainty that this is his eighth. In our case that certainty is missing: if bein hashemashot belongs to the departing day, his birth falls on the Friday. With day eight unproven, the milah cannot be performed on Shabbat.
Sunday, then, is his day, and it may already be day ten of his life. Should that Sunday itself be yom tov, it too is unavailable, because yom tov yields only to a milah that is definitely on day eight, which this one definitely is not. The brit moves to Monday, potentially day eleven. And in a year where the two days of Rosh Hashana come out on Sunday and Monday, the earliest we can circumcise him is Tuesday, which proves to be day twelve of his life: the outer limit our mishnah stated.