Yeshayahu Leibowitz

Yeshayahu Leibowitz was an Israeli scientist, philosopher, Jewish thinker, encyclopedia editor, public teacher and one of the most original and unforgettable voices in the history of the State of Israel. He was a professor at the Hebrew University of Jerusalem in organic chemistry, biochemistry and neurophysiology, a central editor of the Encyclopaedia Hebraica, the author of numerous books on Judaism, science, philosophy, Maimonides, body and mind, religion and state, and a public intellectual who deeply influenced generations of students, readers, listeners and citizens.

Leibowitz’s uniqueness lay in a rare combination of rigorous scientific knowledge, sharp philosophical thought, Orthodox halakhic commitment and an absolute refusal to accept public slogans without examining their meaning. He demanded clear distinctions: between facts and values, science and religion, the state and holiness, worship of God and the satisfaction of human needs, political power and moral responsibility. For this reason he became both deeply admired and fiercely opposed. Yet even his opponents recognized that it is difficult to understand Israeli debates about Judaism, sovereignty, occupation, democracy, science and faith without understanding Yeshayahu Leibowitz.

Childhood in Riga and a religious Zionist family

Leibowitz was born in Riga, then in the Russian Empire and now the capital of Latvia, on January 29, 1903, into a religious Zionist Jewish family. His father, Mordechai Kalman Leibowitz, was a lumber merchant, and his mother, Freida, from the Nimzowitsch family, belonged to an educated Jewish milieu. His younger sister, Nechama Leibowitz, later became one of Israel’s most important teachers and scholars of biblical interpretation. The home in which they grew up combined Torah, Hebrew, general education, European languages and Zionism.

As a child, Leibowitz was educated by private tutors. He spoke Hebrew with his father, Yiddish and German with his mother, and later became fluent in several languages, including Hebrew, Yiddish, Russian, German, English, French and Latin. In youth he encountered broad worlds of literature, science, religion and chess. One of his cousins was Aron Nimzowitsch, one of the great chess players of his era, a family connection that reflects the European-Jewish intellectual world in which he was formed.

In 1919 the family left Riga for Berlin amid the upheavals of the Russian Civil War and the instability of Eastern Europe. The move to Germany placed Leibowitz at the heart of European scientific and academic culture between the two world wars. There his identity took shape as a modern religious Jew, a Zionist, a scientist and a young philosopher.

Berlin, science and philosophy

In Germany, Leibowitz studied chemistry and philosophy at the Friedrich Wilhelm University of Berlin, later Humboldt University. He studied in a first-rate scientific environment, and among his teachers and academic surroundings were major figures in chemistry, physiology and biochemistry. In 1924 he received a doctorate in chemistry, and during this period he worked on the chemistry of sugars and the foundations of organic chemistry.

Alongside chemistry he studied philosophy, and his later thought shows the influence of Immanuel Kant, Maimonides, Karl Popper, Ludwig Wittgenstein and the rationalist Jewish tradition. Already at the beginning of his path, an analytical mode of thought developed in him: define concepts carefully, separate different domains of discourse, and refuse to blur faith, science, morality, politics and emotion.

He later worked at the Kaiser Wilhelm Institute and continued scientific research. He moved to Cologne, studied biochemistry and medicine, and met Greta Winter, who became his wife. The rise of the Nazis and the racial persecution of Jews prevented him from completing his medical studies in Germany, so he moved to Switzerland and completed a doctorate in medicine at the University of Basel in 1934. For him, as for many Jewish intellectuals of his generation, the greatness of European science and the brutality of European antisemitism existed in the same historical world.

Aliyah to the Land of Israel and the Hebrew University

In 1935 Leibowitz immigrated to the Land of Israel and settled in Jerusalem. A year later he began teaching and conducting research at the Hebrew University. He belonged to the generation that built the academic institutions of the Jewish Yishuv and the future State of Israel. At the Hebrew University he worked in organic chemistry, biochemistry, physiology and neurophysiology, and later taught history of science, philosophy of science and general studies.

His chemical research dealt, among other subjects, with sugars and enzymes, and his physiological work addressed the nervous system of the heart. In 1961 he became full professor of organic and biological chemistry and neurophysiology. He retired in 1970, but continued teaching, lecturing and writing for many years. For many students, his university presence was not only that of a laboratory scientist, but of a demanding teacher who asked what science means, what it knows, and what it can never decide.

During the War of Independence, Leibowitz served as a platoon commander in the religious company of the Haganah in Jerusalem. He was also among the early members of a unit that maintained contact with bereaved parents. This chapter shows that he was not only a man of books and laboratories; he lived inside the emerging Israeli reality, with its costs, duties and decisions.

The Encyclopaedia Hebraica and the building of knowledge in Hebrew

One of Leibowitz’s most important projects was his work on the Encyclopaedia Hebraica. He served as editor of the natural sciences section in the early volumes, later became editor-in-chief of central volumes, and wrote many entries. The encyclopedia was a vast cultural undertaking: the creation of a modern Hebrew storehouse of knowledge at a time when Hebrew was again becoming a language of science, statehood, education and public life.

Leibowitz’s contribution to this project grew from the combination of breadth and extreme precision. He demanded conceptual accuracy, factual responsibility, clear writing and serious scientific Hebrew. Even when tensions arose over pace and management, his role in the project shows him as a builder of Hebrew intellectual infrastructure. He did not merely write about science; he helped shape the way modern Hebrew speakers could learn science, philosophy and general culture.

In this sense, Leibowitz belongs to the layer of thinkers and scientists who built Israel’s intellectual tools: university, encyclopedia, public lecture, nonfiction writing, radio conversation and correspondence with readers. He saw knowledge as responsibility, and Hebrew as an essential instrument for the existence of a thinking sovereign Jewish society.

Science, philosophy and the psychophysical problem

Leibowitz devoted much thought to philosophy of science and to the mind-body problem, which he called the psychophysical problem. In his view, human beings do not possess a full rational solution to the relationship between physical processes in the brain and body and subjective mental experiences. Science can describe physiological processes, measure, predict and formulate regularities, but the link between a physical event and inner experience remains an essential mystery of human cognition.

His attitude toward science was deeply respectful but not mystical. Science, for him, is a great rational enterprise of knowing facts. It is subject to method, criticism, experiment and logic. But precisely because he respected science, he opposed turning it into a source of values, religious meaning or moral commands. Science tells us what is; it cannot tell us what ought to be done. This distinction between facts and values became one of the foundations of his thought.

Leibowitz wrote and lectured on evolution, Darwinism, development and heredity, body and mind, science and values, the limits of rationality and the function of concepts. He was one of the people who made basic questions in the life sciences and philosophy of science accessible to Hebrew-speaking audiences without simplifying them into meaninglessness.

Values, needs and the distinction between facts and will

One of Leibowitz’s best-known distinctions is the distinction between value and need. A need is what natural, social or political reality requires a person to take into account. A value, by contrast, is an end that a person chooses and is willing to pay a price to pursue. In his view, there is no scientific or objective standard that can decide which value is correct. Once a person chooses a value, that choice defines his will and his world.

From this came his analysis of different value systems: humanism, nationalism, fascism, anarchism, pacifism, religion, state and army. He sought to show that not all values are compatible. A person can choose the value of religion, humanity, the state or the nation, but must not pretend that there are no tensions among them. For him, many intellectual and moral disasters begin when people sanctify something without admitting that they have made a value choice.

Leibowitz did not try to offer a comfortable and harmonious system. On the contrary, he sought to expose contradictions, costs and decisions. This is one reason his words often sounded harsh. He did not allow the reader or listener to rest in a general love of Judaism, state, science or humanity; he asked what that love means, what it demands and what it may distort.

Judaism as worship of God and observance of commandments

In his religious thought, Leibowitz argued that the essence of Judaism is the worship of God through the observance of commandments. Not belief in the sense of metaphysical opinions, not religious experience, not psychological comfort, not human morality and not national identity stands at the heart of Judaism, but the acceptance of the yoke of Torah and mitzvot. This placed a sharp and unusual position within modern Jewish thought.

For him, worship of God for its own sake means fulfilling the commandments because one accepts the duty to serve God, not for reward, utility, national redemption, social improvement or psychological satisfaction. He opposed explanations of the commandments that turn them into instruments for satisfying human needs. A person who performs a commandment in order to become more moral, healthier, elevated or fulfilled, in his view, is not serving God for God’s sake, but using religion for human purposes.

Leibowitz was deeply influenced by Maimonides, even when his interpretation of Maimonides was controversial. He saw Maimonides as a model of rational Judaism committed to the worship of God and the rejection of idolatry. At the same time, his understanding of Torah, providence, prophecy and messianism was far from many accepted religious views, and therefore generated resistance in religious circles as well as interest and admiration.

Religion and science: two domains that do not compete

Leibowitz rejected the idea that there is a genuine contradiction between science and religion, because in his view they deal with entirely different domains. Science deals with facts about the world: physics, chemistry, biology, evolution, body and matter. Religion, as he understood it, deals with the human being’s standing before God and duty to serve Him. Therefore, a scientific discovery does not threaten faith, and faith should not provide scientific explanations.

He accepted evolution as a scientific fact and did not see it as a religious problem. The Torah, in his view, is not a textbook of natural science or factual history, but a framework of religious demand. When religion tries to replace science, it descends into ignorance; when science tries to dictate values and meaning, it exceeds its boundaries.

This position contributed to Jewish-Israeli discourse because it made possible a form of religiosity that does not fear science, and a form of scientific thinking that does not pretend to solve the question of value. In a society where the tensions among religion, state, modernity and science were strong, Leibowitz offered a severe but fruitful conceptual separation.

The State of Israel, Zionism and separation of religion and state

Leibowitz saw Zionism as a historical opportunity for the renewed political independence of the Jewish people. He was a Zionist, but refused to see the state as a sacred value. The state, for him, is a need: an organizational and political instrument necessary for the existence of a people, but not an object of worship. Only God is holy; not land, not nation, not flag, not army and not government.

From this outlook came his support for the separation of religion and state. He argued that attaching religion to a secular governmental mechanism corrupts religion, turns it into an instrument of politics and desecrates the name of God. He wanted religion to be an independent, demanding and oppositional force, not a department within the state. In this he anticipated many debates that continue in Israel over the rabbinate, kashrut, marriage, education, Sabbath, conversion and religious authority.

His relationship to religious Zionism changed over the years. In his youth he was active in Mizrachi circles and spoke about the possibility of renewing halakha under conditions of Jewish sovereignty. But after the establishment of the state, and especially after the Six-Day War, he became one of the sharpest critics of sanctifying land, nation and state. In his eyes, mixing nationalism with holiness was a dangerous form of idolatry.

Public intellectual and critic of Israeli society

Leibowitz was one of Israel’s outstanding public intellectuals. He wrote articles, gave interviews, delivered lectures, appeared on radio and, above all, spoke in a language that could not be ignored. His lectures in the Broadcast University series made philosophical, scientific and Jewish subjects accessible to a wide audience. Many people came to know him not from an academic article, but from a lecture, conversation or letter.

He frequently answered letters from citizens, students, soldiers, religious Jews, secular Israelis and people in doubt. Some of those letters were published after his death and reveal another side of his personality: not only a sharp speaker and polemicist, but a man willing to answer personal, religious and philosophical questions seriously. His modest home on Ussishkin Street in Jerusalem became a destination for young people and seekers of conversation.

His public style was sharp, sometimes extremely provocative. He said that extreme formulations were meant to awaken the public from indifference. This gave him the nickname “the prophet of wrath of Israeli society.” But behind the wrath stood a method: the demand not to turn power, nation, army, land or leaders into objects of holiness.

The Volunteer Line, nuclear disarmament and civic responsibility

Leibowitz did not remain within abstract thought. In the early years of the state he was active in the Volunteer Line, a civic movement that worked among new immigrants and fought governmental corruption. He saw citizenship not only as loyalty to the state, but also as the duty to criticize it. In years when Mapai’s rule was especially strong, his civic position expressed a healthy suspicion of concentrated power.

In 1962 he was one of the leaders of the Public Committee for Nuclear Disarmament in the Middle East. This activity fits his broader opposition to turning military power into a supreme value. He was not an absolute pacifist, and recognized that a state needs power in order to exist; but he feared militarism, secrecy and the idea that security can justify everything.

In this way, Leibowitz contributed to an Israeli tradition of civic criticism. He rejected the idea that love of country means silence. In his view, precisely concern for the Jewish people and the State of Israel requires criticism, argument and refusal to turn the state into an idol.

After the Six-Day War: the warning about occupation

After the Six-Day War, Leibowitz was among the earliest voices warning against prolonged rule over a large Palestinian population. He understood the Israeli excitement over victory and over the return to the Old City of Jerusalem, but warned that holding the territories would lead to the moral, political and social corruption of Israel. For him, the issue was not only territory but rule over human beings without equal political rights.

He argued that a state ruling a hostile population would inevitably become a secret-police state, distorting education, freedom of expression and the army, and corrupting both rulers and ruled. These warnings, voiced already in the first years after 1967, made him a central figure in the Israeli debate over territories, democracy, morality and security.

Leibowitz used very harsh expressions, some of which generated deep public storms. A contribution-focused profile need not turn his biography into a list of statements, but his influence cannot be understood without recognizing the severity of his warnings. He sought to shock Israeli society so that it would see the price of unlimited power and the danger of turning the army and state into sacred values.

The Israel Prize affair and his refusal

In 1993 the Israel Prize committee decided to award Leibowitz the prize for lifetime achievement and special contribution to society and the state. The decision triggered a public storm because of his political statements, and Prime Minister Yitzhak Rabin announced that he would not attend the ceremony if the prize were awarded to him. Leibowitz, not wishing to turn the ceremony into a state confrontation, announced that he would give up the prize.

The affair illustrates the paradox of his public figure: the state sought to recognize his contribution, but could not contain the full sharpness of his criticism. He himself did not seek official honor, and in many ways was suspicious of turning an intellectual into a state symbol. His refusal became part of his image as someone who preferred fidelity to his position over public recognition.

At the same time, the decision to award him the prize in the first place shows the depth of his influence. Even a society wounded by his words recognized that he had made an extraordinary contribution to education, thought, public debate and Hebrew culture.

Family, students and continuing influence

Leibowitz was married to Greta Leibowitz, a mathematician, and the couple had six children. The wider Leibowitz family became one of Israel’s notable intellectual families: his sister Nechama Leibowitz influenced biblical study; his children and grandchildren worked in science, medicine, law, education, rabbinic life, public affairs and culture. The family itself reflects a Jewish-Israeli combination of Torah, science, criticism and civic responsibility.

Leibowitz died in Jerusalem on August 18, 1994, and was buried at Har HaMenuchot. After his death, his books, letters and conversations continued to appear. Streets were named after him in Israel, his archive was deposited with the National Library, and documentaries, books, studies, articles and polemics continued to deal with his life and thought.

His influence is especially visible in the fact that many of his questions have not disappeared: Is the state a tool or a value? Can religion exist when it depends on government? Can science decide values? Does ruling another people corrupt the ruler? Is Judaism culture, nation, morality or worship of God? The fact that these questions still stand at the center of Israeli discourse is evidence of the depth of his legacy.

Major books and areas of writing

Leibowitz published many books during his lifetime and after his death, some based on lectures and conversations. Among his central works are Judaism, the Jewish People and the State of Israel, Talks on Pirkei Avot and Maimonides, Five Books of Faith, Talks on Science and Values, Body and Mind, The Faith of Maimonides, People, Land, State, I Wanted to Ask You, Professor Leibowitz..., Between Science and Philosophy, and further writings on faith, halakha, philosophy of science, Jewish festivals, the weekly Torah portion and Maimonides.

The importance of these books lies not only in their number, but in the fact that they brought difficult philosophical and Jewish conversation to a broad public. Leibowitz wrote about demanding subjects without surrendering sharpness, and often without softening the reader’s encounter with them. His books do not offer simple comfort; they demand decision, responsibility and thought.

Through this project, Leibowitz became not only a thinker but a school of questioning. He taught readers to distinguish, define, distrust grand words and understand that Judaism and state, science and value, morality and faith are not concepts to be mixed carelessly.

Why this legacy belongs in Moreshet

Yeshayahu Leibowitz merits inclusion in Moreshet because he is one of the figures who shaped modern Jewish-Israeli thought. He connected exact science, Western philosophy, Jewish halakha, modern Hebrew, public criticism and civic responsibility. He contributed to the building of Hebrew knowledge in the Encyclopaedia Hebraica, to scientific and philosophical education at the Hebrew University and in the wider public, and to a piercing Jewish conversation about faith, commandments, statehood, power and holiness.

Moreshet.com documents Leibowitz because Jewish and Israeli heritage is made not only of leaders with whom it is easy to agree, but also of teachers who force a society to think deeply about its most sacred concepts. Yeshayahu Leibowitz’s place in Moreshet rests on his intellectual courage, his influence on generations of students and readers, his contribution to the Hebrew language of science and philosophy, and the questions he left at the heart of Israeli debate: what is Judaism, what is a state, what is a value, and what must never be turned into an idol.