The Gemara says that if R. Eliezer says "Yetaher," he is Tahor once he gets another Nega, even if the Kohen will not see it for seven more days.
I don't understand (especially according to Rashi, who holds that he is not Tahor retroactively). How can the Yisrael decide by himself that the old Nega is Tahor due to the new Nega? This effectively means he is ruling that the new lesion really is a Nega. But only the Kohen may decide this!
Pesach Feldman, Yerushalayim
The simple explanation of this case is that the Kohen already proclaimed the old Nega to be impure, and the Metzora then cut it off. Even though the Rambam in Hilchos Tumas Tzara'as (10:1) rules that a person is liable for cutting a Nega even if the Kohen never saw it, it would not mean that he is impure, and therefore it seems that no fine would apply.
All the best,
Yaakov Montrose
I'm afraid I don't understand the answer. The Rambam rules like Chachamim (he saysso clearly in Perush ha'Mishnayos). My question is in Shitas R. Eliezer, who clearly says thathe is Tamei until he gets another Nega. Why is the Gemara unsure if he holds that the Tumahgoes away once a new Nega comes, even before the Kohen sees it?
Even though the Tumah is only a fine, it seems unreasonable to enact unlike Torah law (which says thatonly a Kohen can rule about Tzara'as), especially to entrust the Tzaru'a himself about this, after hetransgressed Torah law to be Metaher himself prematurely! He could lie and tell people 'I have a new Nega ina private (covered) part of my body, so I am Tahor now.'
Pesach
Firstly, I'm sorry that I had previously misunderstood your question. In fact, your question is included in the question asked by the Mishnah Acharonah in Nega'im (7:4, and discussed here by the Yad Binyamin). He explains that this is a special leniency regarding a Chasan. This is implied by the Gemara saying that it is a practical difference regarding a Chasan. If it would apply to anyone who received a second Nega, then why would the Gemara not say that it applies to everyone? It must be that this is a special leniency regarding a Chasan whom we know has the special leniency according to Torah law not to show a Nega to a Kohen during Sheva Berachos. Accordingly, even if he gets a second Nega during Sheva Berachos he does not have to show it to the Kohen and can be considered Tahor (if it is Yit'har). This also answers your question regarding believing him even though he already transgressed Torah law once regarding this topic.
I would add that people have the ability to lie that they are Tahor whether we would see another Nega or not. He could go on a "business trip" and say he got another Nega and became Tahor, and nobody would be the wiser. I once heard Rav Shlomo Fisher say that this is why the salvation of Bnei Yisrael came about from the "Four Lepers." A bad person who saw he received leprosy would just cut it off, so that he does not have to live outside of the Machaneh and possibly stay there for a long, long time. Someone who goes out of the Machaneh is basically accepting the Din of Hashem, and it is fitting that he should be the bearer of good news to Bnei Yisrael. (It is also possible that this is why Mashi'ach is considered Menuga; see Rashi to Sanhedrin 98a, DH Sovlei.)
B'Birkas ha'Torah,
Yaakov Montrose