and omitted that patient investigation of premises upon which the validity of all argument depends.  They were too fond of systems, and those neatly constructed logical theories into which everything may be fitted admirably—­except the facts.  In addition, the lack of psychological insight which was so common in the eighteenth century tended to narrow their sympathies; and in particular they failed to realize the beauty and significance of religious and mystical states of mind.  These defects eventually produced a reaction against their teaching—­a reaction during which the true value of their work was for a time obscured.  For that value is not to be looked for in the enunciation of certain definite doctrines, but in something much wider and more profound.  The Philosophes were important not so much for the answers which they gave as for the questions which they asked; their real originality lay not in their thought, but in their spirit.  They were the first great popularizers.  Other men before them had thought more accurately and more deeply; they were the first to fling the light of thought wide through the world, to appeal, not to the scholar and the specialist, but to the ordinary man and woman, and to proclaim the glories of civilization as the heritage of all humanity.  Above all, they instilled a new spirit into the speculations of men—­the spirit of hope.  They believed ardently in the fundamental goodness of mankind, and they looked forward into the future with the certain expectation of the ultimate triumph of what was best.  Though in some directions their sympathies were limited, their love of humanity was a profound and genuine feeling which moved them to a boundless enthusiasm.  Though their faith in creeds was small, their faith in mankind was great.  The spirit which filled them was well shown when, during the darkest days of the Terror, the noble Condorcet, in the hiding-place from which he came forth only to die, wrote his historical Sketch of the Progress of the Human Mind, with its final chapter foretelling the future triumphs of reason, and asserting the unlimited perfectibility of man.

The energies of the Philosophes were given a centre and a rallying-point by the great undertaking of the Encyclopaedia, the publication of which covered a period of thirty years (1751-80).  The object of this colossal work, which contained a survey of human activity in all its branches—­political, scientific, artistic, philosophical, commercial—­was to record in a permanent and concentrated form the advance of civilization.  A multitude of writers contributed to it, of varying merit and of various opinions, but all animated by the new belief in reason and humanity.  The ponderous volumes are not great literature; their importance lies in the place which they fill in the progress of thought, and in their immense influence in the propagation of the new spirit.  In spite of its bulk the book was extremely successful;