Talmud - Pesahim 18b פסחים י״ח ב׳

The Gemara asks: And doesn’t the impurity of liquids that came into contact with a creeping animal come from an a fortiori inference: Just as liquids that come to a state of impurity due to contact with a vessel, which itself became impure due to contact with a creeping animal, transmit impurity, with regard to liquids that come to a state of impurity due to contact with a creeping animal, all the more so is it not clear that they transmit impurity to a vessel?

The Gemara answers: Since the basic halakha of these liquids is derived by means of an a fortiori inference, no stringencies are added to it, in accordance with the principle: It is sufficient [dayyo] for the conclusion that emerged from the a fortiori inference to be like the source of the inference. In other words, a halakha derived by means of an a fortiori inference is no more stringent than the source from which it is derived. In this case, liquid that became impure through contact with a creeping animal transmits impurity to the same extent that liquid that became impure through contact with a vessel does.

The Gemara asks: How does Rabbi Akiva interpret the term: Shall be impure, in the first portion of the verse: “From all food which may be eaten, upon which water has come, shall be impure” (Leviticus 11:34)? He interprets the term: Shall be impure, as: Shall render impure. Food transmits ritual impurity to liquids. Do you say that the term teaches that food transmits impurity to liquids, or perhaps the term teaches only that food transmits impurity to a vessel?

The Gemara answers: You can say an a fortiori inference that negates this possibility: Just as liquid, which transmits impurity to food, does not transmit impurity to a vessel, with regard to food, which does not transmit impurity to food, is it not right that it should not transmit impurity to a vessel? If so, how then do I establish the meaning of the term: Shall be impure, which in this context indicates that food impurifies other items? This term indicates that food transmits impurity to liquids, which are susceptible to contracting impurity.

The Gemara asks: Why did Rabbi Akiva mention specifically that food impurifies liquids due to the fact that they are susceptible to contracting impurity? Let him derive this proof from the simple fact that there is no other item that food could render impure. As food does not transmit impurity to food, the only remaining alternative is that food impurifies liquids.

The Gemara answers that this is what Rabbi Akiva is saying: And lest you say that the impurity of food is severe, as evidenced by the fact that it transmits ritual impurity to liquids despite the fact that liquids do not transfer impurity to other liquids, and therefore let food transmit impurity to a vessel, despite the fact that liquid does not transmit impurity to a vessel; therefore, the Gemara states that the fact that food transmits impurity to liquids is actually a stringency characteristic of liquids, not of food. The impurity of food is not more severe than that of liquids; rather, food transmits impurity to liquids due to the fact that liquids are susceptible to contracting impurity.

And in what manner is their susceptibility manifest? It is manifest in the fact that they become ritually impure without being first rendered susceptible to impurity. Foods can become impure only after first coming into contact with one of seven liquids. Liquids do not require any preparatory stage before becoming impure.

Is the principle: Shall be impure teaches that ritual impurity does not render a similar item impure, e.g., that food does not transfer ritual impurity to other food, derived from here? It is derived from there: “But if water is put upon the seed, and any of their carcass falls upon it, it is impure for you” (Leviticus 11:38), from which it is inferred: It is impure; however, it does not transmit impurity to a similar item. Why is an additional source necessary to teach this same principle? The Gemara explains: Both verses are necessary, as one refers to liquids that come to a state of impurity due to contact with a creeping animal, while one verse refers to liquids that come to a state of impurity due to contact with an impure vessel.

The Gemara adds: And both verses are necessary, as neither of the halakhot could have been derived from the other. As, had the verse taught us only the halakha with regard to liquids that come to a state of impurity due to contact with a vessel, one might have thought that liquids do not transfer impurity to similar items only due to the fact that their impurity is not severe, as it did not result from contact with a primary source of impurity; however, with regard to liquids that come to a state of impurity due to contact with a creeping animal, which are impure with a severe form of impurity that resulted from contact with a primary source of impurity, say that they transmit impurity to a similar item.

The Gemara asks: And let the verse teach us that liquids do not transmit impurity with regard to liquids that come to a state of impurity due to contact with a creeping animal, and all the more so will that be the case with regard to liquids that come to a state of impurity due to contact with a vessel. The Gemara answers: This is not difficult, as at times with regard to a matter that could be derived by means of an a fortiori inference, the verse nevertheless unnecessarily wrote it explicitly.

Ravina said to Rav Ashi: But didn’t Rava say that Rabbi Yosei does not hold in accordance with the opinion of Rabbi Akiva with regard to the third-degree ritual impurity status of non-sacred items? Contrary to the opinion of Rabbi Akiva, Rabbi Yosei maintains that an item with second-degree ritual impurity does not confer third-degree impurity status upon non-sacred items by Torah law.

And similarly, Rabbi Akiva does not hold in accordance with the opinion of Rabbi Yosei with regard to the fourth-degree impurity of consecrated property. The relevance of these observations to the issue at hand is that if Rabbi Yosei maintains that the impurity of liquids is by Torah law, he evidently interprets the verse as: Yetamme, just as Rabbi Akiva does. However, in that case, he would also hold that second-degree ritual impurity confers upon another non-sacred item third-degree impurity status, as that halakha is also derived from the term: Yetamme.

Rav Ashi said to him: Rabbi Yosei said this halakha that liquids transmit impurity by Torah law in accordance with the opinion of Rabbi Akiva, his teacher; however, he himself does not hold accordingly, as Rabbi Yosei is of the opinion that liquids do not transmit impurity to other items by Torah law.

Rav Ashi said to Rav Kahana with regard to Rava’s statement: Granted, Rabbi Yosei does not hold in accordance with the opinion of Rabbi Akiva, as it was taught in a baraita that Rabbi Yosei said: From where is it derived with regard to a consecrated item with fourth-degree ritual impurity that it is only disqualified and does not transfer impurity to other objects?

The baraita continues: And this halakha is a logical a fortiori inference: Just as one who lacks atonement, e.g., a zav or leper who immersed at the conclusion of his period of impurity but has not yet brought an offering for his atonement, who is permitted to eat teruma, disqualifies a consecrated item if he comes into contact with it, with regard to third-degree ritual impurity, which disqualifies teruma, and in that way is more severe than one who lacks atonement, is it not right that it should confer fourth-degree ritual impurity status upon a consecrated item? The status of an item with third-degree ritual impurity should be no less severe than that of a person who lacks atonement.

The Gemara notes: And we derived third-degree impurity with regard to consecrated items from the Torah, and fourth-degree impurity of consecrated items by means of the above a fortiori inference. In light of the dayyo principle, one might have thought that this a fortiori inference cannot serve as the basis of the halakha that consecrated property can assume fourth-degree impurity status. Since the source of this inference is third-degree impurity status, the conclusion that emerges can be only that consecrated objects can assume third-degree impurity status, like teruma itself. The Gemara explains that the dayyo principle does not apply in this case. If the a fortiori inference is rendered moot as a result of applying that principle, the principle is not applied. Because the fact that consecrated objects can assume third-degree impurity status is derived from the verse, if that which emerges from the inference is that halakha itself, the a fortiori inference is moot. Therefore, the principle does not apply and the fact that consecrated objects can assume fourth-degree impurity status is derived from the inference.

The Gemara elaborates. The fact that consecrated objects can assume third-degree impurity status is derived from the Torah, as it is written: “And the flesh that touches

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Pesachim 18b explores the dayo principle limiting a fortiori inferences, applied to how impurity transfers between liquids, vessels, and food.