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How Did Chazal Know Science? Moed Katan 11a

How did Chazal know science? The Tannaim and Amoraim in the Talmud frequently make scientific and medical statements, or rule halacha based on an assumed underlying physical reality. Did they conduct experiments, perform dissections and generally observe the world? Did they perhaps study the works of naturalists such as Pliny the Elder? Or, did they derive their scientific knowledge from biblical interpretation? Did their kidneys simply intuit it? Was it part of Oral Law, passed down from Moshe Rabbeinu at Har Sinai? Or, did Hashem grant the righteous Sages Divine inspiration. There is textual basis for many of these claims, and Chazal were not monolithic, so maybe there is no single answer.

Galen, a second-century Greek physician and philosopher, was famously critical of Jews and Christians, writing: “If I had in mind people who taught their pupils in the same way as the followers of Moses and Christ teach theirs—for they order them to accept everything on faith—I should not have given you a definition.” He assumes that all knowledge and authority for Jews is via mesorah. This is clearly not true. Consider Shabbat 151b as one example of many. Rav Pappa said that a lion doesn’t pounce on two people. The Talmud asks הָא קָא חָזֵינַן דְּנָפֵיל? Don’t we see that it does pounce?! True, they resolve Rav Pappa’s statement in a way that he still expresses a truth (based on the attacked people’s spiritual level), but the answer is not “Who are you going to believe? Me or your own eyes?”

Occasionally, the Talmud declares that knowledge was achieved because of Sod Hashem liyre’av (a quote from Tehillim 25:14), that Hashem granted the knowledge to the Sages who fear Him. In Niddah 20b, Rabbi Ami applies this verse to Rabbi Eleazar (b. Pedat) who distinguishes dam niddah from dam chimud by smell, but there is clearly some physical assessment performed there. In Chagiga 3b and Sanhedrin 106b, Rabbi Eleazar and Mar Zutra apply the principle as coming to correct halachic, rather than scientific, conclusions. In Sotah 10a/Sanhedrin 48b, where Rav Nachman describes the sensations of gout, and in Sotah 4a, where the bachelor Ben Azzai describes the timing of the first stage of intercourse, the Talmud itself, rather than a named Amora, gives Sod Hashem liyre’av as one alternative of the source of this knowledge. Alternatives could include personal experience or hearing from a teacher. I don’t know that we can really extrapolate from these examples to say that this is generally true, since it is proffered as a mere alternative, and the Talmudic Narrator sometimes applies concepts enunciated by named Amoraim to new contexts, where it takes on different meaning.

We can point to Rav and Shmuel, first-generation Amoraim who were knowledgeable in various fields of science, and consider how they knew it. Shmuel was an expert in astronomy, and declared that he knew the pathways of heaven like the alleyways of Nehardea, the Babylonian town over which he presided (Brachot 58b), and that he was capable of fixing the calendar for the entire Diaspora (Rosh Hashanah 20b). The author of Chikrei Lev suggested that Shmuel learned astronomy from the gentile astronomer/astrologer Avlet (where the discipline had recently come to the Greeks from India), but Rav Aharon Hyman rejects this, since this discipline was known/important to Jews for ages.

Shmuel was an expert in embryology, more than others (Niddah 25b). He had comprehensive knowledge of cures (Bava Metzia 113b), and indeed cured Rav of intestinal suffering (Shabbat 108a). When Tannaim argue about a woman’s physical signs of maturity, Shmuel weighs in to clarify Rabbi Yossi HaGelili’s position. We are told how Shmuel gained this knowledge—via direct observation, and he recompensed the Canaanite maidservant, who was his subject, four dinar for her embarrassment. He didn’t simply intuit this knowledge via Divine inspiration, but actively sought it out.

Rav was also quite knowledgeable in certain sciences. He went to a cemetery, performed some action, and declared that 99% died because of the evil eye and only one by natural means; whereas Shmuel declared that every injury is due to wind (germs) entering wounds and bodily cavities (Bava Metzia 107b). (Hyman considers this evidence of Rav’s scientific knowledge.) He discusses the importance of wearing shoes (to prevent cold) and eating meat after a bloodletting (Shabbat 129a). He declares that for six to 12 days, a fevered person is sustained (from his own fats) without eating (Sanhedrin 108b). He knew details of the water cycle (Shabbat 145b). These lists aren’t comprehensive.

Rav apprenticed himself to a shepherd for 18 months, to learn to distinguish between permanent and temporary blemishes in sheep (Sanhedrin 6b), thus showing a willingness to learn from a specialist and via direct observation. We see the same in our sugya (Moed Katan 11a). Rav relates several statements told to him by Adda Tzayada (the catcher/fisherman). For instance, a fish close to its spoiling is best. (We don’t presume that Adda was trying to move old inventory.) Or, that the best way to prepare and consume fish is with related substances (broiled with salt, placed in water, consumed with fish brine, followed with a drink of water). Adda advised exercise and following certain fish meals with water or beer but not wine. Note that Adda possesses no rabbinic title, but Rav hearkened to him and conveyed his specialist teachings.


Rabbi Dr. Joshua Waxman teaches computer science at Stern College for Women, and his research includes programmatically finding scholars and scholastic relationships in the Babylonian Talmud. 

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