At the age of twenty-eight Diderot conceived the plan of that “Encyclopædia” which became the central activity of his life. A few years later he published his first work, a free translation of Shaftesbury’s “Essay on Merit and Virtue,” which indicates well the philosophical point from which he set out. It was followed, a year after, by the “Pensées Philosophiques,” a few brief pages, full of condensed and vigorous satire on the theologians and of robust faith in man and nature. Perhaps the most memorable is that in which he imagines that a man, betrayed by his wife, his children, his friends, retired into a cavern to meditate some awful revenge against the human race, a perpetual source of dread and misery; at last the misanthrope rushed out of his cavern shouting. “God! God!” and his fatal desire was accomplished: this account of the matter at all events indicates how little, even at this early period of his life, Diderot sympathized with the fashionable Deism of his day. The book was condemned to be burned by command of Parliament, but it was subsequently reinforced by still more audacious additions. So began characteristically, if with something of the reckless impetuosity of youth, a series of writings, far too long even to name here, many that were only published at his death, some that are only now being published, a large number that have probably been lost altogether--all marked by the same prodigious wealth and variety and eloquence. Yet they lie apart from the great work of his life. The “Encyclopædia” occupied thirty years; the appearance of the first volume was retarded by Diderot’s imprisonment at Vincennes, and it appeared in 1751; the last appeared in 1772. The “Encyclopædia” was more than an encyclopædia; it was not founded on that of Chambers, by which it was suggested, nor is it represented by our own estimable “Encyclopædia Britannica.” It was not a simple summary of the knowledge of the time, for the benefit of a community trained to appreciate the value of science. It was in the words of the prospectus, “a general picture of the efforts of the human spirit in every field, in every age.” It was the frank and audacious application to the whole of knowledge of new ideas, for the first time loudly proclaimed to a society slowly crumbling to ruin, but still by no means powerless. It was an evangelistic enterprise among infidels, with dangers on every side, and where one holds one’s life in one’s hands. We may still appreciate the significance of such a struggle. The future in every age belongs to those who can see further ahead than their fellows, and who fight their way towards the vision that they see; but the risks are equally great under any condition of society, and some sort of Bastille or Vincennes is always at hand.