Mishnah 8 in chapter 3 of Maseches Eduyos continues the series of disputes that were taught in the vineyard at Yavneh between a particular Tanna and the Sages. This time the focus is on Rabbi Tzadok, one of the outstanding figures of the closing years of the Second Temple period, who fasted for forty years. Regarding him too, disputes were taught in which he ruled tamei while the Sages were lenient and ruled tahor.
"Shloshah devarim Rabbi Tzadok metamei v'Chachamim metaharin" - three things Rabbi Tzadok declares susceptible to tumah and the Sages declare not susceptible:
"Masmer hashulchani" - the shopkeeper's nail:
This refers to the nail used by the storekeeper. It is a metal nail, nothing more than a sort of metal sliver. Now, metal utensils do not need a receptacle in order to become susceptible to tumah, but they do need to perform some function - a utensil that carries out a defined task. An ordinary nail, the kind you drive into a wall to hang things on, is not considered a utensil at all; it is too basic.
This nail, however, is attached to the cabinet and serves as a kind of pivot on which the pan of the scale rests, so that one can see which side is heavier. That is an important function, and the question is twofold: first, is such a function enough to make it a utensil, given that there is nothing distinctive about it and any other object could have served the same purpose? Second, since it is attached to a cabinet used for storage, is it merely part of the cabinet, so that its tumah status depends on the cabinet, or does it have an independent existence as a utensil in its own right?
Rabbi Tzadok holds that it has a life of its own: it counts as part of the weighing mechanism, and therefore it stands on its own, separate from the cabinet. It performs only a simple action in fulfilling its function, and even so it becomes susceptible to tumah in its own right. The Sages say: it is nothing more than part of the cabinet, and it does not become tamei on its own - if the cabinet becomes tamei, it becomes tamei along with it, and if not, it remains tahor.
"Aron shel grusos" - the bin of the bean grinders:
This is the storage chest used by those who grind beans into meal. The rule is that wooden utensils become susceptible to tumah when they have a receptacle, and a storage chest certainly has a receptacle. However, large vessels do not become susceptible to tumah in two situations: when they cannot be moved while full, or when from the outset they were meant to remain in one place - once they have been set down and built into their spot, the intention is that they stay there, and they are therefore "made to rest" (asuyim l'nachas).
That is the case before us: under normal circumstances a person does not move the storage chest for bean flour, and it stays where it is, from which it follows that it does not become susceptible to tumah. But when it needs repair, the accepted practice is that the bean grinder brings the chest to the carpenter rather than bringing the carpenter to the chest. So on these rare occasions it actually is moved - there is no concern that it will break on the way; it really is carried. The question is whether this amount of moving is enough to classify it as a portable utensil, or whether, since it is meant to remain in place under normal circumstances, it is "made to rest" and does not become susceptible to tumah.
Rabbi Tzadok is stringent and says that it does become susceptible to tumah, while the Sages say that since it is meant to stay in place most of the time, it does not become susceptible to tumah.
"Masmer shel sha'os" - the nail of the hours:
This is the nail used to cast a shadow on a sundial. The sundial is made of stone, with the hours of the day marked on it; depending on the position of the sun in the sky, a shadow is cast and moves over the course of the day, and from the position of the shadow one can tell the time. The shadow is cast by a small metal nail.
The question is whether this counts as a defined enough function for the object to be considered a vessel. On the one hand, it serves as a kind of clock - an effective device for measuring time. On the other hand, anything at all could fill that role; even a splinter of wood would do, and there is nothing that requires specifically this metal nail.
Rabbi Tzadok says that it is susceptible to tumah, since this is the nail by which the time is measured. The Sages say that this is not enough: casting a shadow is not a distinctive function, because anything casts a shadow, and there is nothing special about this plain metal rod. Therefore it is not considered a vessel and it does not become susceptible to tumah.
In summary: in all three cases - the moneychanger's nail, the grain dealer's chest, and the nail used for telling the hours - Rabbi Tzadok rules that the item is susceptible to tumah and the Sages rule that it is not. And in all of these cases the halachah, as is generally the rule, was decided in accordance with the Sages.