Yadayim, Chapter 4, Mishnah 7. As our masechta nears its end, the Mishnah preserves several open confrontations between the Tzedukim and the Perushim. The Tzedukim rejected the authority of Torah shebe'al peh, while the Perushim carried the tradition that is ours. The pattern of each exchange is the same: the Tzedukim point to what looks to them like a contradiction among the rulings of the Chachamim, and the Perushim respond, usually by demonstrating that the very same difficulty rebounds upon those who raised it. Our mishnah preserves two such rounds, the first in the field of tumah and taharah, the second in the laws of nezikin.
The column of poured liquid
The Tzedukim begin: "Kovlin anu aleichem Perushim" - we lodge a complaint against you, Perushim, since you declare a nitzok to be tahor.
What exactly is a nitzok? It is not a river or brook, but the arc of liquid suspended between two vessels at the moment one is being emptied into the other. The Bartenura directs us to where this halachah is taught: in Machshirin the rule is given as "kol hanitzok tahor," that such a poured column carries no tumah with it. The practical case: someone pours from a vessel that is tahor into a vessel that is tamei. Whatever liquid is still in the upper vessel remains tahor, since "nitzok eino chibur," the descending stream does not create a halachic bond joining the two vessels. The tumah of the lower vessel cannot climb the column and reach what has not yet left the upper one. It was this leniency that the Tzedukim held up as objectionable.
The reply: a conduit leaving a burial ground
The Perushim answer using the identical formula of complaint, this time against the Tzedukim: they declare tahor a water conduit, an "amas hamayim," whose course runs out from a cemetery. Here the subject genuinely is moving water, water that has traveled through a place of burial and is nonetheless not pronounced tamei.
The Bartenura explains where the strength of the retort lies: the Tzedukim themselves grant that this water keeps its taharah ("modu ba Tzedukim detehorah"), relying on the words of the pasuk in Vayikra, "mikveh mayim yihyeh tahor," that a gathering of water stays pure. The Perushim, then, are not simply hurling a counter-accusation. They are showing that their own position hangs together: water that has never been detached and made susceptible in the way the halachah demands does not contract tumah, and this holds equally for a stream being poured and for a channel emerging from a graveyard. The party whose approach wobbles is the one that is lenient in the second instance while insisting on stringency in the first.
Oxen, donkeys, and household servants
A second protest follows from the Tzedukim, this time about your teaching, Perushim, that an owner must pay when his ox or his donkey does damage, while a master owes nothing when his eved or his shifchah does damage.
They present it as a kal vachomer. Toward an animal a person bears no mitzvah obligations whatsoever, and still the damage it does is charged to its owner. Toward a servant a master certainly does bear mitzvah obligations. Should it not follow, all the more so, that the damage done by a servant is charged to the master? The argument appears to move from the lighter case upward to the weightier one.
The Perushim reject the inference with a single word: "lo," no. What may be said of an ox and a donkey cannot be said of a servant, because the animal has no da'as while the servant does. Cattle do not deliberate or decide, and therefore the accountability for their damage rests with the one who owns them. A servant has a mind of his own and chooses his own actions. Were the master to be held liable, the results would be unbearable: annoy such a servant, provoke his anger, and he need only walk out, put a torch to a neighbor's stack of grain, and leave the payment to his master.
The Bartenura fills in the picture vividly: a servant nursing a grudge could bankrupt the man who owns him, running up losses of a hundred maneh every single day, knowing all the while that the account would be settled by somebody else. It is exactly because the servant possesses da'as that the halachah lays the liability at his own door. That placement is what removes any incentive to wreck property out of resentment, and it is why the servant simply cannot be measured against the animal.
Both grievances of the Tzedukim in this mishnah thus fall apart under scrutiny. The halachos of the nitzok rest on a principle the Tzedukim themselves accept, and a master's exemption from his servant's damage grows directly out of the very trait that separates a human being from a beast: the ability to think and to choose.