Science and the Talmud

The Talmudic approach to the sciences, from astronomy to botany.

The rabbis of the Talmud molded Jewish law and practice, but they also took note of scientific ideas and the world around them. They made observations, tested their hypotheses, and classified their results. This was, in large part, because it helped them know how to perform the mitzvot most accurately. In order to apply the mitzvot of the Torah to the world–the chief project of the Talmud–the rabbis had to know the world.

A survey of the Talmud turns up frequent discussions of botany, anatomy, biology, zoology, astronomy, medicine, magic, astrology (which would have been regarded as "science"), and even rudimentary chemistry. Although they were not engaged in sophisticated scientific calculations, the rabbis demonstrated a remarkable awareness of various branches of scientific study.

Religion and science are often seen as being in conflict. In general, the former makes claims based on faith; the latter on reason and method. But because the religion of the Talmud is concerned with practice more than dogma, this dichotomy is rarely addressed.

Driven by practicality and their own curiosity, there were times that the rabbis did what would be called science for its own sake, as a means to understand the way the world operated. This may have helped them do mitzvot more accurately, but that was not always their chief concern.


One of the most important endeavors for the rabbis in talmudic times was setting the calendar and the holidays. This depended on a significant understanding of astronomy, and many of the talmudic sages became experts in this field. Using observations of the new moon, Samuel bar Abba was able to calculate and determine the calendar and the dates of holidays many years in advance, and even accounted for leap years (Rosh Hashana 20b).


Judaism is often described as an embodied religion–the practices depend on the physical performance of the commandments. The rabbis tried to become intimately aware of the ways that the body works, in order to more fully understand how to observe the commandments.

Many commandments assume a properly functioning and classifiable body, and so the rabbis also had to account for human anomalies–blindness, deafness, muteness, late development, and double or no sex-organs. For example, they considered whether a deaf person could blow the shofar for a hearing person to discharge their obligation on Rosh Hashanah (Rosh Hashanah 29a).

The rabbis’ extensive concern with purity led them to carefully study labor, menstruation, miscarriage, and male procreative functions. This familiarity allowed the rabbis to fit people into categories and determine which obligations applied to which types of people. The rabbis thus concluded the ways in which an intersex person was similar and dissimilar to a man. Could an intersex person marry? Were they obligated to fulfill the commandments? Were their mothers in a state of impurity after their birth as they are with a boy or with a girl? (Mishna Bikkurim 4:1-2).

The commandment of pikuah nefesh (saving a life), is taken very seriously, and the science of medicine permeates the pages of the Talmud. Yevamot 64b prohibits circumcising a child with hemophilia, for example. Medicine was also practiced in order to return "quality of life," as when the rabbis describe the performance of cranial surgery on an affliction called Ra’atan (Ketubot 77b), which  prevented a man from fulfilling his marital duties.

Still, it would be an overstatement to suggest that the rabbis’ anatomical curiosity was only related to performing the commandments. The Talmud reports that the students of Rabbi Yishmael dissected a deceased prostitute, causing them to reconsider the belief that the body had 248 joints and limbs (Bekhorot 45a). In another similar incident Rabbi Haviva and Ravina dissected an ewe to decide whether it was suffering from a hip disease or a severed spinal chord (Hullin 51a). What is remarkable about these instances is that they seem to have been undertaken independent of any desire to perform the mitzvot more accurately.


The vast lists of plants, trees, and flowers mentioned in the Talmud read almost like a botanical guide to ancient Babylonia. The rabbis categorized the flora around them, often to illuminate both legal and non-legal biblical passages but sometimes seemingly for its own sake.

Fruits that came from trees, as opposed to those that came from the ground, received different blessings. The Talmud reports their extensive investigation to determine what plants grow where. Some major mitzvot required knowledge of botany, such as the commandment to shake a lulav–a bouquet of palm, willow, and myrtle–and to cover a sukkah with agricultural material. What was allowed to cover a sukkah? From where exactly was one to take the palm branch for the lulav?

On  Shavuot, Jews were to bring the firsts of their produce to Jerusalem. But what counted as first fruits? Maror, bitter herbs, were to be eaten on Passover. What kinds of lettuces fulfilled the obligation of maror? All of these required botanical investigations.

Biology & Genetics

The rabbis believed that certain activities conducted by parents could affect the child prior to conception and in utero. In Nedarim 20a-b, the rabbis suggest that the nature of copulation could affect the health of the infant. Once conceived, they believed other behaviors such as smelling an etrog or working in a tannery could  positively or adversely affect the child (Ketubot 60b-61a).

The Talmud also considers the question of whether prayer can help to determine the gender of an unborn baby. The rabbis reject this possibility in Berakhot 60a:

Has not Rabbi Isaac the son of Rabbi Ammi said, If the man first emits seed, the child will be a girl; if the woman first emits seed, the child will be a boy?

Although their understanding of genetics and biology was incorrect, their refusal to link prayer to sex determination implies a positioning of the physical world as distinct from the spiritual in this matter.

Zoology/Animal Behavior

In addition to human traits, animal behavior was also a concern of the talmudic rabbis. For example, the end of Shabbat was determined by the appearance of three stars. The rabbis ask, "What happens if the skies are cloudy and one cannot see any stars?" One is directed to watch the fowls descend from their perches or the ravens fly from the fields (Shabbat 35b). When they do, night had arrived and Shabbat was over.

The Talmud also reports rabbis trying to explain animals and their behavior as mysteries of the world, independent of their contribution to halakhah:

Rabbi Zera met Rav Judah standing by the door of his father-in-law’s house and saw that he was in a cheerful mood, and if he would ask him all the secrets of the universe he would disclose them to him. He asked him: Why do goats march at the head of the flock, and then sheep after them? He said (quoting a scriptural verse): It is as the world’s creation, darkness first and then light…. Rabbi Zera asked: Why is a camel’s tail short? Because it eats thorns and a long tail would get stuck in the thorns. Why is an ox’s tail long? Because it grazes in meadows and has to beat off the gnats with its tail…. (Shabbat 77b)

What is striking about this passage is that at first the Torah is invoked in order to explain animal behavior, but then the explanations about the other animals seamlessly move to that which is observable in the world independent of any commandment. The world is not only explainable through the Torah, but also through observation, hypothesis, and confirmation.

All in all, it is difficult to suggest one attitude towards science in the Talmud. Its vastness contains what seem to be attitudinal contradictions. There are times that the rabbis encounter scientific theories that compete with their own understanding, forcing them to discard theories and revise their worldview. But, there are other instances where they decide that their understanding is right because it is based on something that is revealed to them.

Since Jewish law is not based on the Talmud alone, when contemporary science and the scientific understanding in the Talmud conflict, one cannot assume that Jewish law should be revised. Other considerations may compel the law to stay the same, despite the "errors" upon which it seems to be based. Because there is an understanding that science, by its nature, is always provisional, more authority is given to the process of deciding Jewish law, than the facts themselves, scientific or otherwise, upon which decisions are made.

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