He was born in Dessau. His father's name was Mendels and he later took the surname Mendelssohn ("son of Mendel"). Mendel Dessau was a poor scribe--a writer of scrolls--and his son Moses in his boyhood developed curvature of the spine. His early education was cared for by his father and by the local rabbi, David Fränkel. The latter, 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.
His life was a struggle against crushing poverty, but his scholarly ambition was never relaxed. A refugee Pole, Zamosz, taught him mathematics, and a young Jewish physician was his tutor in Latin. He was, however, mainly self-taught. He learned to spell and to philosophize at the same time (Graetz). With his scanty earnings he bought a Latin copy of John Locke's "Essay concerning the 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 he was appointed by a wealthy silk-merchant, Isaac Bernhard, as teacher to his children. Mendelssohn soon won the confidence of Bernhard, who made the young student successively his book-keeper and his partner.
Gumperz or Hess rendered a conspicuous service to Mendelssohn and to the cause of enlightenment in 1754 by introducing him to Lessing. Just as the latter afterwards makes Nathan the Wise and Saladin meet over the chess-hoard, so did Gotthold Lessing and Mendelssohn actually come together as lovers of the game. The Berlin of the day--the day of Frederick the Great--was in a moral and intellectual ferment. Lessing was the great liberator of the German mind. He had already begun his work of toleration, for he had recently produced a drama (Die Juden, 1749), the motive of which was to prove that a Jew can be possessed of nobility of character. This notion was being generally ridiculed as untrue, when. Lessing found in Mendelssohn the realization of his dream. Within a few months of the same age, the two became brothers in intellectual and artistic cameraderie. Mendelssohn owed his first introduction to the public to Lessing's admiration. The former had written in lucid German an attack on the national neglect of native philosophers (principally Gottfried Leibniz), and lent the manuscript to Lessing. Without consulting the author, Lessing published Mendelssohn's Philosophical Conversations (Philosophische Gesprache) anonymously in 1755. In the same year there appeared in Danzig an anonymous satire, Pope a Metaphysician (Pope ein Metaphysiker), which turned out to be the joint work of Lessing and Mendelssohn.
From this time Mendelssohn's career was one of ever-increasing brilliance. He became (1756-1759) the leading spirit of Nicolai's important literary undertakings, the Bibliothek and the Literaturbriefe, and ran some risk (which Frederick's good nature obviated) by criticizing the poems of the king of Prussia. In 1762 he married Fromet Gugenheirn, 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, although among the competitors were Thomas Abbt and Immanuel Kant. In October 1763 the king granted Mendelssohn the privilege of Protected Jew (Schutz-Jude)--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 the Phädon (1767). Modelled on Plato's dialogue of the same name, Mendelssohn's work possessed some of the charm of its Greek exemplar. What most impressed the German world was its beauty and lucidity of style--features to which Mendelssohn still owes his popularity as a writer. The Phädon was an immediate success, and besides being often reprinted in German was speedily translated into nearly all the 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 is no exaggeration to assert with Kayserling 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. Lavater was one of the most ardent admirers of Mendelssohn. He described him as "a companionable, brilliant soul, with piercing eyes, the body of an Aesop--a man of keen insight, exquisite taste and wide erudition . . . frank and open-hearted." Lavater was fired with the ambition to convert his friend to Christianity. In the preface to a German translation of Bonnet's essay on Christian Evidences, Lavater 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". Bonnet resented Lavater's action, but Mendelssohn was bound to reply, though opposed to religious controversy. As he put it: "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."
Mendelssohn shared his pragmatism with Lessing; it is probable that the latter was indebted to Mendelssohn. The consequences of Lavater's intrusion into Mendelssohn's affairs were that the latter resolved to devote the rest of his life to the emancipation of the Jews. Among them secular studies had been neglected, and Mendelssohn saw that he could best remedy the defect by attacking it on the religious side. A great chapter in the history of culture is filled by the influence of translations of the Bible. Mendelssohn added a new section to this chapter by his German translation of the Pentateuch and other parts of the Bible. This work (1783) constituted Mendelssohn the Martin Luther of the German Jews. From it, the Jews learned the German language and imbibed culture; with it there came a new desire for German nationality; its popularity resulted in a new system of Jewish education. Some of the conservatives among the Jews opposed these innovations, but the current of progress was too strong for them. Mendelssohn was the first great champion of Jewish emancipation in the 18th century. He it was who induced CW Dohm to publish in 1781 his epoch-making work, On the Civil Amelioration of the Condition of the Jews, a memorial which played a great part in the triumph of tolerance. Mendelssohn himself pqblished a German translation of the Vindiciae judaeorum by Menasseh ben Israel.
The excitement caused by these proceedings led Mendelssohn to publish his most important contribution to the problems connected with the position of Judaism in relation to the general life. This was the Jerusalem (1783; Eng. trans. 1838 and 1852). It is a forcible plea for freedom of conscience, described by Kant as "an irrefutable book." Its basic thrust is that the state has no right to interfere with the religion of its citizens. Kant called this "the proclamation of a great reform, which, however, will be slow in manifestation and in progress, and which will affect not only your people but others as well." Mendelssohn asserted the pragmatk principle of the possible plurality of truths: that just as various nations need different constitutions--to one a monarchy, to another a republic, may be the most congenial to the national genius--so individuals may need different religions. The test of religion is its effect on conduct. This is the moral of Lessing's Nathan the Wise, the hero of which is undoubtedly Mendelssohn. The parable of the three rings is the epitome of the pragmatic position. One direct result of this pragmatism was unexpected. Having been taught that there is no absolutely true religion, Mendelssohn's own descendants--a brilliant circle, of which the musician Felix was the most noted--left the Synagogue for the Church.
Despite this, Mendelssohn's theory was a strengthening bond in Judaism. For he maintained that Judaism was less a "divine need, than a revealed life." In the first part of the 19th century, the criticism of Jewish dogmas and traditions was associated with a firm adhesion to the older Jewish mode of living. Reason was applied to beliefs, the historic consciousness to life. Modern reform in Judaism is parting to some extent from this conception, but it still holds good even among the liberals.
In Mendelssohn's remaining years, he progressed in fame, numbering among his friends many of the greatest men of the age. His Morgenstunden appeared in 1785, and he died as the result of a cold contracted while carrying to his publishers in 1786 the manuscript of a vindication of his friend Lessing, who had predeceased him by five years.
Mendelssohn had six children. His sons were: Joseph (founder of the Mendelssohn banking house, and a friend and benefactor of Alexander Humboldt), whose son Alexander (d. 1871) was the last Jewish descendant of the philosopher; Abraham (who married Leah Bartholdy and was the father of Fanny Hensel and J. L. Felix Mendelssohn-Bartholdy); and Nathan (a mechanical engineer of considerable repute). His daughters were Dorothea, Recha and Henriette, all brilliantly gifted women.