Mistakes about science

Today's daf talks about spontaneously generated lice. There's a dispute among tannai'm whether you can kill a louse on Shabbat (Shabbat 12a, 107b). Rav Yosef explains that the disagreement only applies to insects that "do not reproduce," but killing all other insects is forbidden (107b). The rishonim then discuss which species of insect are generated from sweat, from rot, from dirt, etc., or from eggs. The halakhah concludes that killing lice is permitted.

There are much more dramatic Torah-versus-science issues out there than this one. If you're looking for explosive controversy, you want evolution. If you're looking for out-of-date science in the Talmud, this collection is just a start; Pesahim 94b is a big one in particular. If you're looking for a legal and moral mess, look into organ donation.

But, even if relatively undramatic, the issue of spontaneous generation is centrally important to science versus Halakhah. It's unique as a black-and-white case of a canonized halakhah based on rejected science.

Much has already been written about how to handle this (I googled it for you; also, Rav Natan Slifkin has about 30 posts on it), so I'll just bother to quickly summarize the approaches and then pick my favorite. I'll cite each approach using the name with which it seems most associated nowadays.

Opinions that change the halakhah, so now you may not kill the lice:

• Rav Yosef Shalom Elyashiv: The Talmud's lice may have been different from our lice.
• Rav Yitzhak Lampronti (Pahad Yitzhak): The science behind this halakhah is wrong, so we should be stringent.

Opinions that keep the halakhah, so you still may kill the lice:

• Lubavitcher Rebbe: We cannot prove that the sceince behind this halakhah is wrong. Lack of evidence of spontaneous generation is not negative proof.
• Rav Eliyahu Dessler: The halakhah preceded the explanation. The Talmud's explanantion was wrong, so we find a new explanation, but we don't question the halakhah itself.
• Rav Shlomo Zalman Auerbach: The Talmud didn't mean actual spontaneous generation, but rather the appearance of it to the naked eye.
• Rav Moshe Shmuel Glasner (Dor Revi'i): The science behind this halakhah is wrong, but once it has been canonized by the Talmud, we may not overturn it.

I think that each of these opinions contains important insights for approaching challenges in general. For the specific issue of spontaneous generation, I'm most persuaded by the Dor Revi'i.

The difficulty with the Dor Revi'i, in contrast to all the other approaches, is that we end up following a halakhah that we acknowledge is wrong. I've heard Rav Herschel Shachter dismiss the Dor Revi'i in favor of Rav Shlomo Zalman for this reason: were the halakhah indeed based on a mistake, we should throw out the halakhah!

I'm nobody to dispute Rav Schachter, but in this case the evidence appears strong that the halakhah was indeed based on a mistake. All the amora'im and rishonim understood the halakhah as being based on literal spontaneous generation, which was a universally accepted fact from Aristotle until the Scientific Revolution.

But then, if it's a mistake, do you throw out the halakhah or not? There's precedent for "not." The Dor Revi'i cites the Mishneh Torah, Hilkhot Shehitah 10:12–13, regarding the list of terefot, fatal conditions in an animal.

Quoth the Rambam:

ואין להוסיף על טריפות אלו כלל. שכל שאירע לבהמה או לחיה או לעוף חוץ מאלו שמנו חכמי דורות הראשונים והסכימו עליהן בבתי דיני ישראל אפשר שתחיה. ואפילו נודע לנו מדרך הרפואה שאין סופה לחיות:

וכן אלו שמנו ואמרו שהן טריפה אף על פי שיראה בדרכי הרפואה שבידינו שמקצתן אינן ממיתין ואפשר שתחיה מהן אין לך אלא מה שמנו חכמים שנאמר על פי התורה אשר יורוך:

We may not add to [the preceding list] of fatal conditions, whatsoever. For after any incident that happens to a domesticated animal, wild animal, or bird, it's possible that it will survive, except for those fatal conditions that were listed by the earliest Sages and agreed upon by the courts of Israel. This is even if we know, based on medical knowledge, that they cannot live.

And so too, any conditions they listed as fatal, even if we see in our current medical knowledge that some of them do not die, and it's possible that the animal will live—we have nothing but what was listed by the Sages, as is said, "According to the law that they instruct you." 

That's the core of the argument by the Dor Revi'i. I think similar reasoning even underlies the Pahad Yitzhak. His decision to "change the halakhah" in light of science is a stringency based on doubt—fundamentally, he's still inclined to keep the halakhah. In the Torah world, the caution in touching a precedent is like that of touching a live wire.

I note further that Rav Yitzhak ha-Levi Herzog, the teacher of both Rav Elyashiv and Rav Auerbach, followed the Dor Revi'i regarding lice.

Finally, about halakhah and truth:

I know that many people would be disturbed by the thought of keeping a halakhah that is fundamentally untrue. For that objection, we have the important agadta on tannuro shel Akhnai (see Bava Metzi'a 59b), where even a voice from the sky couldn't sway the halakhah. "It is not in heaven"—by handing the Torah over to man and not the angels, God knowingly and gladly made a decision to sacrifice absolute truth for human practice. We know from the beginning that there will be mistakes, and once those mistakes are canonized, the canon—meaning everything passed from tanna'im to amora'im to rishonim to posekim—remains the will of God.

I confess that there are reasons to nitpick (haha, pun!) about applying that principle to an empirical mistake, and so you need the justifications given by the Dor Revi'i. But at least for me, tannuro shel Akhnai takes the force out of the complaint "but it's wrong!"

חדש טוב!

Update: After reading about him here, here, and especially here, I have come to the conclusion that the Dor Revi'i was the man. His kever is on Har ha-Zeitim, across Har ha-Bayit from where I'm sitting at this moment.

Update, 10/21/2012: Here's a touchier example, from Sefer ha-Mitzvot:

והמצוה הקע"ז היא שהזהירנו מאכול השרצים המתהוים מן העפושים אע"פ שאינו מין ידוע ולא יתהוה מזכר ונקבה. והוא אמרו (שם) ולא תטמאו את נפשותיכם בכל השרץ הרומש על הארץ. ולשון ספרא השרץ הרומש על הארץ אע"פ שאינו פרה ורבה. וזה הוא ההפרש בין אמרו השרץ השורץ על הארץ ובין השרץ הרומש על הארץ. כי השרץ השורץ הוא השרץ שיש בו הכח המוליד לדומה כי הוא ישריץ על הארץ והשרץ הרומש הוא השרץ המתהוה מן העפושים שלא יוליד הדומה לו. ומי שאכל ממנו גם כן כלום לוקה:

The opinions of Rav Dessler and Rav Auerbach are safer here than that of Dor Revi'i. The Dor Revi'i would have to say that the Sifra got a mitsvah de-orayta wrong and led major rishonim to miscount the taryag mitsvot. That's a bit messy, but sometimes the truth is messy.

As for the opinions of Rav Elyashiv and Rav Schneerson, I cannot accept the premise that any animal ever has or ever will spontaneously generate. It would require a huge fluke of entropy, which just won't happen.

Update, 10/22/2012: In Sacred Monsters, Rav Slifkin also cites tannuro shel Akhnai to reconcile the halakhah with scientific mistakes. "The Talmud itself attests to the concept that legal authority takes precedence over objective truth." He ties that directly to Rav Herzog on lice. I'm not sure the connection is so direct, but nonetheless, barukh she-kivvanti.