In serious compositions, or in satires, the French thinkers of the eighteenth century--the whole body of Materialists--had revealed the hollowness of the doctrine, in which the so-called civilized peoples had found comfort and tranquillity for many centuries. The world was deprived of a God, the heavens were enshrouded in mist; all that had hitherto seemed firm and incapable of being displaced was turned topsy-turvy. The doctrine of Jesus had lost its power of attraction, and become degraded in the eyes of the earnest and thoughtful to the level of childish fables. Infidelity had become a fashion. With the undeifying of Jesus appeared to go hand-in-hand the dethronement of God, and doubt of the important dogma of the immortality of the soul, which Christian theology had borrowed from Greek philosophy and, as always, adorning itself with strange feathers, had claimed as its original creation. Thereupon depended not merely the confidence of mankind in a future existence, but also the practical morals of the present. If the soul is mortal and transient, they thought in the eighteenth century, then the acts of man are of no consequence! Whether he be good or evil, virtuous or criminal, on the other side of the grave there was no retribution. Thus, after the long dream of many centuries, the civilized portion of mankind again fell into the despondency prevalent in the Roman society of the empire; they were without God, without support, without moral freedom, without stimulus to a virtuous life. Man had been degraded to a complicated machine. Mendelssohn was also biased by the prejudice that the dignity of man stands and falls with the question of the immortality of the soul. He therefore undertook to restore this belief to the cultured world, to discover again the lost truth, to establish it so firmly and ward off materialistic attacks upon it so decisively, that the dying man should calmly look forward to a blissful future and to felicity in the after-life. He composed a dialogue called "Phædon, or the Immortality of the Soul." It was to be a popular book, a new doctrine of salvation for the unbelieving or sceptical world. Therefore he gave to his dialogue an easily comprehensible, attractive style, after the pattern of Plato's dialogue of the same name, from which he copied also the external form. But Plato supplied him with the mere form. Mendelssohn caused his Socrates to give utterance to the philosophy of the eighteenth century through the mouth of his pupil, Phædon.