Moses Mendelssohn was born in Dessau. His father's name was Mendel, and it was Moses who adopted the surname Mendelssohn ("Mendel's son"). Moses's son Abraham Mendelssohn wrote in 1829 (to Felix), "My father felt that the name Moses Ben Mendel Dessau would handicap him in gaining the needed access to those who had the better education at their disposal. Without any fear that his own father would take offense, my father assumed the name Mendelssohn. The change, though a small one, was decisive."
Mendel was an impoverished scribe — a writer of Torah scrolls — and his son Moses in his boyhood developed curvature of the spine. Moses's early education was cared for by his father and by the local rabbi, David Fränkel, who besides teaching him the Bible and Talmud, introduced to him the philosophy of Maimonides. Fränkel received a call to Berlin in 1743. A few months later Moses followed him.
A refugee Pole, Israel Zamosc, taught him mathematics, and a young Jewish physician taught him Latin. He was, however, mainly self-taught. He learned to spell and to philosophize at the same time (according to the historian Graetz). With his scanty earnings he bought a Latin copy of John Locke's An Essay Concerning Human Understanding, and mastered it with the aid of a Latin dictionary. He then made the acquaintance of Aaron Solomon Gumperz, who taught him basic French and English. In 1750, a wealthy silk-merchant, Isaac Bernhard, appointed him to teach his children. Mendelssohn soon won the confidence of Bernhard, who made the young student successively his bookkeeper and his partner.
It was possibly Gumperz who introduced Mendelssohn to Gotthold Ephraim Lessing in 1754, who became one of his greatest friends. It is said that the first time Mendelssohn met Lessing, they played chess. In Lessing's play Nathan the Wise Nathan and the character Saladin first meet during a game of chess. Lessing had recently produced the drama Die Juden, whose moral was that a Jew can possess nobility of character. This notion was, in the contemporary Berlin of Frederick the Great, generally ridiculed as untrue. Lessing found in Mendelssohn the realization of his dream. Within a few months, the two became closely intellectually allied. Lessing also brought Mendelssohn to public attention for the first time: Mendelssohn had written an essay attacking Germans' neglect of their native philosophers (principally Gottfried Leibniz), and lent the manuscript to Lessing. Without consulting the author, Lessing published Mendelssohn's Philosophical Conversations (Philosophische Gespräche) anonymously in 1755. In the same year there appeared in Danzig (now Gdańsk, Poland) an anonymous satire, Pope a Metaphysician (Pope ein Metaphysiker), which turned out to be the joint work of Lessing and Mendelssohn.
Early prominence as philosopher and critic
Mendelssohn became (1756–1759) the leading spirit of Friedrich Nicolai's important literary undertakings, the Bibliothek and the Literaturbriefe, and ran some risk (which Frederick's good nature mitigated) by criticizing the poems of the King of Prussia. In 1762 he married Fromet Guggenheim, who survived him by twenty-six years. In the year following his marriage Mendelssohn won the prize offered by the Berlin Academy for an essay on the application of mathematical proofs to metaphysics, On Evidence in the Metaphysical Sciences; among the competitors were Thomas Abbt and Immanuel Kant, who came second. In October 1763 the king granted Mendelssohn, but not his wife or children, the privilege of Protected Jew (Schutzjude), which assured his right to undisturbed residence in Berlin.
As a result of his correspondence with Abbt, Mendelssohn resolved to write on the immortality of the soul. Materialistic views were at the time rampant and fashionable, and faith in immortality was at a low ebb. At this favourable juncture appeared Phädon oder über die Unsterblichkeit der Seele (Phaedo or On the Immortality of Souls; 1767). Modelled on Plato's dialogue of the same name, Mendelssohn's work possessed some of the charm of its Greek exemplar and impressed the German world with its beauty and lucidity of style. Phaedo was an immediate success, and besides being one of the most widely read books of its time in German was speedily translated into several European languages, including English. The author was hailed as the "German Plato," or the "German Socrates"; royal and other aristocratic friends showered attentions on him, and it was said that "no stranger who came to Berlin failed to pay his personal respects to the German Socrates."
So far, Mendelssohn had devoted his talents to philosophy and criticism; now, however, an incident turned the current of his life in the direction of the cause of Judaism. In April 1763, Johann Kaspar Lavater, then a young theology-student from Zurich, made a trip to Berlin, where he visited the already famous Jewish philosopher with some companions. They insisted on Mendelssohn telling them his views on Jesus and managed to get from him the statement, that, provided the historical Jesus had kept himself and his theology strictly within limits of orthodox Judaism, Mendelssohn "respected the morality of Jesus' character." Six years later, in October 1769, Lavater sent Mendelssohn his German translation of Charles Bonnet's essay on Christian Evidences, with a preface where he publicly challenged Mendelssohn to refute Bonnet or if he could not then to "do what wisdom, the love of truth and honesty must bid him, what a Socrates would have done if he had read the book and found it unanswerable." Mendelssohn answered in an open letter in December 1769: "Suppose there were living among my contemporaries a Confucius or a Solon, I could, according to the principles of my faith, love and admire the great man without falling into the ridiculous idea that I must convert a Solon or a Confucius." The ongoing public controversy cost Mendelssohn much time, energy and strength.
Lavater later described Mendelssohn in his book on physiognomy, "Physiognomische Fragmente zur Beförderung der Menschenkenntnis und Menschenliebe" (1775–1778), as "a companionable, brilliant soul, with piercing eyes, the body of an Aesop [who was traditionally considered ugly]—a man of keen insight, exquisite taste and wide erudition [...] frank and open-hearted"—ending his public praise with the wish of Mendelssohn recognizing, "together with Plato and Moses... the crucified glory of Christ." When, in 1775 the Swiss-German Jews, faced with the threat of expulsion, turned to Mendelssohn and asked him to intervene on their behalf with "his friend" Lavater, Lavater, after receiving Mendelssohn's letter, promptly and effectively secured their stay.
In March 1771 Mendelssohn's health deteriorated so badly that Marcus Elieser Bloch, his doctor, decided his patient had to give up philosophy, at least temporarily. After a short and restless sleep one evening, Mendelssohn found himself incapable of moving and had the feeling of something lashing his neck with fiery rods, his heart was palpitating and he was in an extreme anxiety, yet fully conscious. This spell was then broken suddenly by some external stimulation. Attacks of this kind recurred. The cause of his disease was ascribed to the mental stress due to his theological controversy with Lavater. However, this sort of attack, in milder form, had presumably occurred many years earlier. Bloch diagnosed the disease as due to 'congestion of blood in the brain' (a meaningless diagnosis in modern medical practice as such congestion is anatomically impossible), and after some controversy this diagnosis was also accepted by the famous Hanoverian court physician, Johann Georg Ritter von Zimmermann, an admirer of Mendelssohn. In retrospect, his illness might be diagnosed as a heart-rhythm-problem (such as atrial fibrillation) and/or a mild form of familial dysautonomia, a hereditary disease of Ashkenazi Jews, which often brings with it a curvature of the spine and epilepsy-like symptoms in times of stress.
Mendelssohn was treated with China bark, blood lettings on the foot, leeches applied to the ears, enemas, foot baths, lemonade and mainly vegetarian food. “No mental stress whatsoever” was ordered. However, although he remained subject to periods of setback, he eventually recovered sufficiently to write the major works of his later career.
Mendelssohn died on January 4, 1786 as the result (it was thought at the time) of a cold contracted while carrying a manuscript (his reply to Jacobi, titled To Lessing's Friends (An die Freunde Lessings)) to his publishers on New Year's Eve; Jacobi was held by some to have been responsible for his death. He was buried in the Jewish Cemetery of Berlin. The translation of the Hebrew inscription on his gravestone (see picture below, right) reads: H[ere] r[ests] / the wise R[eb] Moses of Dessau / born on the 12th of Elul 5489 [September 6, 1729] / died on Wednesday the 5th of Shevat [January 4] / and buried the next morning on Thursday 6th/ 5546 [January 5, 1786] / M[ay] H[is] S[oul be] B[ound up in the] B[ond of eternal] L[ife] Although the cemetery was largely destroyed during the Nazi era, after German reunification, in 2007-2008, it was reestablished with monuments to its past, including a recreation of Mendelssohn's gravestone.