Traditional Jewish theology affirms the belief in an omniscient deity. As formulated in Maimonides’ thirteen articles of faith, the creator “knows all the deeds of human beings and all their thoughts.”
In the idiom of biblical Hebrew, one of the most common ways to express the idea that God has access to our innermost thoughts and desires is by means of expressions like Jeremiah’s “I the Lord search the heart, I test the kidneys.”
Those readers who are more familiar with the classic King James English version might be better acquainted with the wording “I try the reins.” That, however, is not an allusion (figurative or otherwise) to the straps that are used to restrain a horse, but is rather an obsolete synonym for the kidney, derived from the Latin “renes,” the same root that gives us English derivatives like “renal,” and even “adrenalin.”
The premise that underlies those expressions is that the kidney, like the heart, is a locus of thought, emotion and especially moral judgment—a conception that may have originated in ancient Egypt. Of course, scientific physiology has long since reassigned those mental functions to the brain, which did not figure very prominently in that capacity in ancient literatures; although it is the cardiac blood-pump that continues to provide the favourite metaphors for love in valentine cards, bumper stickers and emojis.
Perhaps it is possible to write off those scriptural phrases as nothing more than convenient examples of interior parts of the human anatomy, an approach that was indeed favoured by Rabbi Abraham Ibn Ezra. The rabbis of the Talmud, however, were clearly of the opinion that the expressions were to be understood with literal precision. In a passage that enumerates the functions of the various human organs, no distinction is made between biological, mental or emotional functions, and the power of counsel is ascribed to the kidneys. A midrashic homily speculates that Abraham, who had no access to human teachers in his heathen environment, must have learned the Torah from the wisdom that was housed in his own kidneys.
More specifically, the Talmud taught: “A person possesses two kidneys. One of them advises him for good and one advises him for evil. It stands to reason that the good one is on one’s right side and the evil one on the left, as it is written, ‘A wise man's heart is at his right hand; but a fool's heart at his left.’” I like to imagine them as those little figures of a halo-topped angel and a pitchfork-wielding devil who argue out moral decisions in cartoons.
Most rabbinical scholars in the medieval Sephardic and Italian realms received a thorough medical or philosophical training; so it would eventually come to their attention that the prevailing scientific theories did not support the traditional Hebrew understanding of the kidneys’ functions.
As a rule, discrepancies of this sort did not provoke severe theological dilemmas among the faithful. After all, Maimonides had long since declared that the scientific pronouncements of the ancient rabbis should not necessarily be accepted dogmatically, since they were not essential parts of the received Torah tradition, but merely reflected the sages’ personal opinions or the scientific theories that were current in their environment. However, this solution could not be easily invoked for the kidney question, since its earliest source was not in the Talmud or Midrash, but in the Bible itself. We therefore find that several rabbis had to make special efforts to uphold the claim that the kidneys are a source of human thought and counsel.
This problem became particularly acute in Renaissance Italy. New experimental methods in medical research were overthrowing the long-entrenched systems of Aristotle and Galen.
Rabbi Moses Provençal of Mantua (1503–1576) was asked how to reconcile the rabbinic statements about the kidney with the tenets of contemporary physicians and biologists who spoke of the brain as the centre of intellect and judgment. In his responsum, the rabbi submitted that in this case the teaching of the Jewish sages is to be preferred. To be sure, the scientists may be forgiven for getting it wrong; after all, unlike the sages of Israel, they do not enjoy the benefits of an unbroken chain of tradition that extends back via the biblical prophets and elders to the divine revelation at Mount Sinai.
In a very similar vein, his contemporary Rabbi Isaac Lampronti observed that even though the achievements of medical science might appear very impressive to us, their work is of necessity limited to observable phenomena; but as long as they are unable to grasp every aspect of the innumerable details that constitute reality, they will not have truly penetrated into the deeper meanings of the processes they are describing. As regards the specific topic of human biology, the secular scientists do not fully understand the systems of nourishment and growth, or the sources of bodily strength and vigor.
Rabbi Lampronti therefore viewed the purely empirical knowledge of the scientists as essentially superficial, to be contrasted with the profound wisdom of the Jewish sages who were privy to the divine secret of creation. “Anyone who is intimately familiar with it will be capable of achieving wonders that are far more numerous than what the scientists can boast—wonders that they can accomplish by means of the science of alchemy or through natural magic.”
Rabbi Lampronti noted that of all the internal organs, the kidneys are the only ones that come in pairs. This ties in neatly with the Talmud’s statement about how they serve to advise the lone heart to pursue either virtuous or sinful options. The Talmud’s linking of the two kidneys with the good and evil inclinations supports those interpreters who regard the kidneys’ impact as rooted in sexual desire—which can take the form either of participation in wholesome family life or of destructive promiscuity.
On further reflection, the linking of thoughts and moods with internal physical organs does not strike me as inherently irrational. True, for centuries western thinking was dominated by the doctrine of “Cartesian dualism” (named for French philosopher René Descartes) and its conviction that the human mind is an abstract entity that is essentially independent of the physical body that houses it. However, traditional religious thought, especially the kind that found expression in medieval Jewish moralistic writings, maintained a more nuanced approach, observing that the health or illness of one’s body can exert a powerful influence on a person’s intellectual abilities. Rationalists like Maimonides insisted that we must follow a strict moral discipline in order to rein in biological urges that are constantly tempting us away from our spiritual or intellectual missions.
Current medical science is more cognizant of how human behaviour can be influenced by the activities of various glands, hormones or drugs that are secreted or processed by internal organs. While there is no evident indication that the kidneys are counted among the organs that affect our reasoning, there was no prima facie reason for pre-moderns to rule such ideas out of hand.
Judah Halevi touched on this matter briefly in his Kuzari arguing that the relationship between the kidneys and human intelligence is analogous to the impact of physiological masculinity on men’s cognitive functions. In a definitive expression of chauvinism and political incorrectness, Halevi did not make reference, as a modern writer would likely have done, to testosterone-inspired belligerence or violence, but rather to the indisputable fact (according to the science of his time) that eunuchs are observably less intelligent—even when compared to creatures of limited intellectual capacity, such as... women (who also happen to be incapable of growing beards)!
Somehow I have a gut feeling (on the right side, of course) advising me that I should not accept such views unquestioningly.