Zavim, Chapter 1, Mishnah 1. With this mishnah we open Maseches Zavim, one of the masechtos of Seder Taharos. The masechta rests on a handful of foundational concepts that return again and again from beginning to end, so it pays to absorb them carefully here at the start. In these opening mishnayos they will be spelled out at length; later on a brief mention will be enough to recall them.
First, the subject itself. A zav is a male who experiences a particular kind of discharge, a flux. It is crucial to distinguish it from an ordinary seminal emission. Regular semen leaves the body from a living, erect member, and that produces the status of a ba'al keri, a different matter entirely. The discharge that concerns our masechta issues from an eiver meis, a limp organ. That is the flow the Torah calls zov.
A single sighting
The starting point is the plainest situation imaginable. "Haro'eh re'iyah achas", a man who sees one emission, "shel zov", of flux, and nothing further. Where does that leave him? "Beis Shammai omrim": the school of Shammai holds that his position resembles that of a "shomeres yom k'neged yom", a woman required to keep watch over one day set against another. "U'Veis Hillel omrim": the school of Hillel likens him instead to a "ba'al keri".
Beis Shammai compares him to a shomeres yom k'neged yom: he must watch one day against the day of his flow. Practically, this means that whatever he lies upon and whatever he sits upon becomes tamei. He is certainly not yet a zav gamur, a full-fledged zav, for that requires flow over three days; still, in the view of Beis Shammai, even a single drop already carries the power to transmit tumah. And should it later emerge that his condition is in fact the more serious one, then retroactively, lemafre'a, the various items he sat upon are treated as impure as well, all on the strength of that one drop of flux.
Beis Hillel takes the opposite line. This man is classified together with a ba'al keri, and a ba'al keri conveys no tumah whatsoever to his bedding or to his seat. Accordingly, even if he should move a drop of the flux, his own taharah is unaffected. Everything shifts only when a second discharge appears; from that point onward he is handled as a zav with the power to defile objects. But so long as nothing beyond a lone emission has occurred, Beis Hillel maintains that no tumah passes from him at all, and it is exactly here that Beis Shammai parts company with him.
A flow, a clean day, then a double flow
The next case has more moving parts. The wording runs: "ra'ah achas", he saw one emission; "u'vasheini hifsik", on day two the flow stopped; "u'vashlishi ra'ah shtayim", and on day three there were two, "o achas merubah kishtayim", or one that stretched out to the measure of two. "Beis Shammai omrim": in their view he is a zav gamur. "U'Veis Hillel omrim": he is "metamei mishkav u'moshav", defiling what he lies and sits upon, and "v'tzarich bi'as mayim chayim", living water is required, yet "pattur min hakorban", no korban is due. Several distinct points are folded into this ruling, and each deserves separate treatment.
Here is the sequence. Day one brought a single emission. Day two brought none. Day three brought either two separate emissions or one continuous flow whose length is counted as two. And how long must a flow last before it counts double? The measure is yitbol v'yisnageiv: the span a person needs in order to go down, immerse himself, and towel off afterward. Chazal quantified it more precisely as the time needed to cover a distance of fifty amos, something on the order of fifty meters. A discharge lasting that long is no longer a lone re'iyah; halachah reckons it as shtei re'iyos.
On these facts Beis Shammai calls the man a zav gamur, and that status carries with it a chiyuv korban. Their reasoning: the emission of day one links up with the pair from day three, and the barren middle day poses no obstacle to that linkage. Since day three furnished two, his tally comes to three emissions, and three emissions place a man under the obligation of a korban.
Beis Hillel arrives at a different result. In his ruling the man is "metamei mishkav u'moshav": bedding and seats that bear his weight become tamei, so to that extent he does hold the standing of a zav. He also needs bi'as mayim chayim, entry into living water, and the objects he made use of must be brought into such water as well. A korban, however, he does not owe. The reason is that for Beis Hillel the first day's emission does not fuse with the drawn out flow of the third. A full twenty four hours passed in the middle with nothing at all, and that empty day functions as a divider. What is left, then, is a pair of emissions, and two emissions of zov carry no korban obligation. Beis Shammai, by contrast, counts backward across the gap and takes in the emission of two days earlier.
Rebbi Elazar ben Yehuda redraws the dispute
A qualification is now recorded in the name of Rebbi Elazar ben Yehuda: "modim Beis Shammai", the school of Shammai itself agrees, "bazeh she'eino zav gamur", that in this very case the man has not reached the status of a full zav. The intervening day, after all, cancels out the emission of day one, exactly along the lines set out above in Beis Hillel's reasoning.
If that is so, the mishnah raises the natural question, al mah nechlaku: where does the dispute actually lie? Beis Shammai would then be voicing the very same ruling as Beis Hillel. Comes the answer: the argument is "al haro'eh shtayim", about one who saw two, "o achas merubah kishtayim", or a single one drawn out to the measure of two, "u'vasheini hifsik", and on the second day the flow ceased, "u'vashlishi ra'ah achas", and on day three he saw one. There "Beis Shammai omrim": he is a zav gamur.
Rebbi Elazar is supplying a correction of scope. The machlokes, he holds, is confined to the reverse sequence. Two emissions came first, or one extended emission equivalent to two (a flow lasting the interval of fifty amos, as described above), then a completely dry second day, and then a further single emission on day three. In that configuration Beis Shammai pronounces him a full zav.
What lies behind that? From the moment two emissions have occurred, the man already stands subject to a count of shiv'ah nekiyim, seven days free of flux. Since that obligation is already upon him, a day that passes without any discharge is not viewed as breaking anything off. His total is therefore three emissions, three re'iyos, and that makes him a zav gamur who owes a korban.
Beis Hillel, as Rebbi Elazar frames the dispute, still holds that the man is "metamei mishkav u'moshav", defiling whatever bears his weight lying or sitting, and that bi'as mayim chayim is called for here, all on account of the two re'iyos he genuinely had. The korban, though, he does not owe: once the count of two is complete, the later single emission fails to attach itself to them, since a flux free day fell between. And absent a full set of three re'iyos there is no korban at all. Beis Shammai, as explained, treats all three as one continuous tally and obligates him to bring it.
Two structural ideas emerge from this mishnah and will accompany us onward: the difference between a partial zav status, which transmits tumah to mishkav and moshav, and the full status of a zav gamur, which carries the obligation of a korban; and the question of whether a clean day interrupts the count or is swallowed up within it. These will be our companions throughout the masechta.