Moses Mendelssohn

Early Life in Dessau and Arrival in Berlin

Moses Mendelssohn was born on September 6, 1729, in Dessau, in the principality of Anhalt, the son of a Torah scribe named Mendel Heymann. He received a thorough traditional Jewish education, studying the Talmud under Rabbi David Fränkel, whose commentary on the Jerusalem Talmud he helped carry when Fränkel moved to Berlin in 1743. The young Moses — fourteen years old and walking much of the way — followed his teacher to the Prussian capital.

Berlin in 1743 was a city of contrasts. Frederick the Great presided over a court animated by French culture and Enlightenment ideas, while the Jewish community lived under severe legal restrictions. Mendelssohn arrived almost penniless and initially survived on charity from Fränkel's congregation. He educated himself prodigiously, learning German, Latin, Greek, English, French, mathematics, and philosophy — in particular the rationalist systems of Leibniz and Wolff — largely on his own.

Intellectual Formation and Friendship with Lessing

In 1750, Mendelssohn became a tutor in the household of the silk manufacturer Isaac Bernhard, eventually becoming bookkeeper and then business partner. This position granted him the precarious legal status of a 'protected Jew' (Schutzjude) — a permit that allowed him to reside in Berlin but could be revoked at any time.

The most consequential event of Mendelssohn's intellectual life came in 1754, when he met Gotthold Ephraim Lessing, already the most brilliant young writer in Germany. The two became intimate friends and collaborators. Lessing, recognizing Mendelssohn's philosophical gifts, arranged for the anonymous publication of his Philosophical Conversations (Philosophische Gespräche, 1755), a defense of Leibnizian philosophy. Lessing also wrote his famous play Nathan the Wise (1779) with Mendelssohn as the model for its protagonist — a wise, tolerant Jew who embodies Enlightenment humanity.

Mendelssohn's Letters on Sentiments (Briefe über die Empfindungen, 1755) established him in German literary circles as a philosopher of aesthetic experience. His essay On Evidence in Metaphysical Sciences (Über die Evidenz in Metaphysischen Wissenschaften, 1764) won the first prize of the Berlin Academy — defeating, among others, Kant's essay on the same subject — and made him famous across Europe.

The Phaedon and Popular Fame

In 1767, Mendelssohn published Phaedon, or On the Immortality of the Soul — a modernization of Plato's Phaedo in which the ancient arguments for the soul's immortality are supplemented and revised in light of Leibnizian rationalism. Written in elegant German prose and explicitly designed for a cultivated non-specialist audience, the Phaedon was an immediate sensation, translated into French, English, Dutch, Italian, Danish, Russian, and Hebrew. It made Mendelssohn the most widely read German philosopher of the 1770s, celebrated across Europe as 'the German Socrates.'

The book's central arguments turn on the simplicity and unity of the soul (it cannot be dispersed like matter, therefore it cannot die), its essential activity as a thinking substance, and the moral and teleological order of creation that demands the soul's continued perfection after death.

The Lavater Affair and Jewish Identity

In 1769, the Zurich pastor Johann Caspar Lavater publicly challenged Mendelssohn either to refute the arguments of the Christian apologist Charles Bonnet — which Lavater had just translated into German and dedicated to Mendelssohn — or to convert to Christianity. The challenge put Mendelssohn in an impossible position: to argue publicly against Christianity risked inflaming Christian public opinion, while conversion was unthinkable.

Mendelssohn's reply — composed with extraordinary delicacy — declined to engage in public religious polemic while defending Judaism as a religion of reason and revelation. The episode crystallized his thinking about the relationship between Judaism and rational religion, and he thereafter devoted increasing energy to defending Jewish intellectual dignity and arguing for Jewish civil rights.

Biblical Translation and the Haskalah

In the 1780s, Mendelssohn undertook his most ambitious project: a new German translation of the Pentateuch (with Psalms and other books added later), accompanied by a Hebrew commentary (Biur). The translation was printed in Hebrew characters — allowing Jews who could not read German script to acquire German — and was designed simultaneously to bring Jews into contact with German culture and to demonstrate to Germans the literary and philosophical depth of the Hebrew scriptures. It became the founding text of the Haskalah — the Jewish Enlightenment — shaping generations of Jewish intellectuals from Heine to Freud.

Jerusalem and the Philosophy of Religion and Politics

Mendelssohn's Jerusalem, or On Religious Power and Judaism (1783) is his philosophical masterpiece. Responding to an anonymous pamphlet that seemed to challenge the consistency of his public positions, Mendelssohn developed a comprehensive argument in two parts.

The first part argues for the separation of church and state: civil society rests on property rights and social contract; it may use coercive means to enforce its aims. Religion, by contrast, pertains to convictions and actions addressed to God; because genuine religious belief cannot be coerced, the state has no legitimate authority over religious life. Neither church nor state may excommunicate citizens or deprive them of civil rights on religious grounds.

The second part argues that Judaism is not a religion in the sense of revealed doctrine — it contains no revealed dogmas that members must believe on pain of exclusion. Instead, Judaism is a system of revealed legislation — a divine law governing the actions of the Jewish people — combined with a natural religion accessible to all rational human beings. This distinction allowed Mendelssohn to argue that Jews could be full citizens of Enlightenment states (whose public sphere was governed by natural religion and rational ethics) while continuing to observe the particular laws of their tradition in private.

Jerusalem was immediately recognized as a masterpiece of Enlightenment political thought. Kant praised it as 'the proclamation of a great reform.'

Final Years and the Pantheism Controversy

In his final years, Mendelssohn was drawn into the Pantheismusstreit (Pantheism controversy) ignited by F.H. Jacobi's claim that Lessing had privately confessed to Spinozism. Mendelssohn, defending his late friend's reputation, published Morning Hours (Morgenstunden, 1785), arguing against Spinozism and for the rationalist theism he had always defended. He died on January 4, 1786, exhausted by the controversy, still working on his reply to Jacobi.

Legacy

Mendelssohn's legacy is multiple and contested. As philosopher, he was among the last great representatives of Leibniz-Wolffian rationalism, a significant aesthetician, and the author of a political theology that anticipated later liberal arguments for religious toleration. As Jewish intellectual, he personified — and helped create — the possibility of Jewish participation in European culture. His grandson was Felix Mendelssohn Bartholdy, the composer.

The trajectory of his family — Felix was baptized, and Moses's own children largely abandoned Judaism — became for many the symbol of the tragic cost of assimilation. Gershom Scholem and others have debated whether Mendelssohn's compromise between Enlightenment universalism and Jewish particularity was intellectually coherent or inherently unstable. Regardless of how one answers this question, Mendelssohn remains an indispensable figure for understanding the modern encounter between Judaism and Western modernity.