The "Lettres philosophiques" may be considered the first of Voltaire's polemic writings. They exhibit his mordant wit, his clear-sightedness and his moral courage. There is in them, perhaps, more real gayety, more spontaneous fun, than in his later books. Voltaire was between thirty-five and forty years old when they were written, and although he possessed to the end of his long life more vitality than most men, yet he was physically something of an invalid, and his many exiles and disappointments told upon his temper. From 1734, when these letters first appeared in France, to 1778, when he died, worn out with years, labors, quarrels, and honors, his activity was unceasing. He had many followers and many enemies, but hardly a rival. Voltaire was and is the great representative of a way of looking at life; a way which was enthusiastically followed in his own time, which is followed with equal enthusiasm to-day. This view he expressed and enforced in his numberless poems, tragedies, histories, and tales. It formed the burden of his voluminous correspondence. As we read any of them, his creed becomes clear to us; it is written large in every one of his more than ninety volumes. It may almost be said to be on every page of them. That creed may be stated as follows: We know truth only by our reason. That reason is enlightened only by our senses. What they do not tell us we cannot know, and it is mere folly to waste time in conjecturing. Imagination and feeling are blind leaders of the blind. All men who pretend to supernatural revelation or inspiration are swindlers, and those who believe them are dupes. It may be desirable, for political or social purposes, to have a favored religion in the state, but freedom of opinion and of expression should be allowed to all men, at least to all educated men; for the populace, with their crude ideas and superstitions, may be held in slight regard.