The tum’ah of avodah zarah

Shabbat 82a–83b discusses the rabbinically instituted tum’ah of avodah zarah. The mishnah starting the ninth perek quotes the opinion of Rabbi Akiva, that the tum’ah is like that of a niddah:

משנה. אמר רבי עקיבא: מניין לעבודה זרה שמטמאה במשא כנדה - שנאמר +ישעיהו ל+ תזרם כמו דוה צא תאמר לו, מה נדה מטמאה במשא - אף עבודה זרה מטמאה במשא.

The Gemara then quotes a mishnah from Avodah Zarah 47a with Hakhamim who differ, and compare the tum’ah to that of a sherets:

תנן התם: מי שהיה ביתו סמוך לעבודה זרה ונפל - אסור לבנותו. כיצד יעשה - כונס לתוך שלו ארבע אמות ובונה. היה שלו ושל עבודה זרה - נידון מחצה על מחצה. אבניו ועציו ועפריו מטמאים כשרץ, שנאמר +דברים ז+ שקץ תשקצנו וגו’. רבי עקיבא אומר: כנדה, שנאמר +ישעיהו ל+ תזרם כמו דוה, מה נדה מטמאה במשא - אף עבודה זרה מטמאה במשא.

It’s really helpful to have the picture of darkhei hittamme’ut straight when learning this sugya. I would have been quite unprepared had I not written a post on this material before. Even more helpful is the chart in the Encyclopedia Talmudit, in the article on טמאה, column 479, which unfortunately I can’t reproduce here.

Some of the things that are helpful to know:

• A zavah, niddah, and yoledet are metamme’ot in the following ways: magga, massa, heset, derisah, even mesama, and bi’ah.
• A nevelat behemah is metamme’ah through magga and massa only. I also can’t help but note the case of nevelat of tahor, which is only metamme’ah through swallowing, and not even magga.
• A sherets is metamme through magga only.

Then the question that the Gemara needs to clarify is which forms of contact the tanna’im were talking about when they compared the tum’ah de-rabban of avodah zarah to the tum’ah de-orayta of niddah and sherets.

The simplest peshat is that the tanna’im meant that the comparisons are full. In other words, Rabbi Akiva holds that avodah zarah is metamme’ah through magga, massa, and even mesama, and the Hakhamim hold only through magga. But for some reason no amora’im understand them that way.

There’s Rabbah, who bumps the Hakhamim in a more mahmir direction, to include massa:

ואמר רבה: במשא - דכולי עלמא לא פליגי דמטמאה, דהא אתקש לנדה. כי פליגי - באבן מסמא; רבי עקיבא סבר: כנדה, מה נדה מטמאה באבן מסמא - אף עבודה זרה מטמאה באבן מסמא. ורבנן סברי: כשרץ, מה שרץ לא מטמא באבן מסמא - אף עבודה זרה לא מטמאה באבן מסמא.

And then there’s Rabbi Elazar, who bumps Rabbi Akiva in the mekil direction, excluding even mesama:

ורבי אלעזר אמר: באבן מסמא - דכולי עלמא לא פליגי דלא מטמאה, כי פליגי - במשא. רבי עקיבא סבר: כנדה, מה נדה מטמאה במשא - אף עבודה זרה מטמאה במשא, ורבנן סברי: כשרץ, מה שרץ לא מטמא במשא - אף עבודה זרה לא מטמאה במשא.

I can find no explanation for what motivated Rabbah and Rabbi Elazar to not take the tanna'im at face value. Nothing in Mesivta or Artscroll, so I take it that all the mefarshim took this for granted. The Gemara discusses how the tanna’im work out the hekeshim according to the understanding of each amora, but I think the Gemara could have worked them out for the simplest peshat of the mishnah too if it had too. (Which is another question: to what extent are the asmakhtot here post facto?)

I must be missing something.

Update, 12/26/2012: I went through this gemara more carefully with a sho'el u-meshiv. We came up with an even stronger question.

What does the Gemara mean by the objection ולוקשה רחמנא לנבלה?

Peshat seems to be, that if the Hakhamim were right about avodah zarah transferring through masa and even mesama, then the Bible could have skipped the hekeshim to sherets and niddah and just given us a hekesh to nevelah. But this is a din de-rabbanan, and the hekeshim are asmakhtot. Why should the Torah and navi conform to a later rabbinic decree? The logic seems totally out of order. That's kind of what I meant when I threw out the post facto business yesterday, but expressed much more sharply.

It turns out that the Penei Yehoshua asks both of our questions: first, why do we assume that Rabbi Akiva and the Hakhamim each go beyond the one hekesh they give in the mishnah, and second, how to understand ולוקשה רחמנא לנבלה? It's a relief to see your kashyot confirmed by one of the mefareshim!

He explains the Gemara here based on the Yerushalmi, which learns the hekeshim differently, and in fact has a hekesh to nevelah (not explicitly, but the Penei Yehoshua works one out). The Yerushalmi also, in fact, understands the tum'ah of avodah zarah to be de-orayta. The Penei Yehoshua then fits this all together. But his mehalekh opened up new questions for us. So I think I'm going to leave this post here for now.