During the whole of the Middle Ages, under the bloody despotism of the popes, atheism was persecuted with fire and sword as a most pernicious system. As the "godless" man is plainly identified with the "wicked" in the Gospel, and is threatened--simply on account of his "want of faith"--with the eternal fires of hell, it was very natural that every good Christian should be anxious to avoid the suspicion of atheism. Unfortunately, the idea still prevails very widely. The atheistic scientist who devotes his strength and his life to the search for the truth, is freely credited with all that is evil; the theistic church-goer, who thoughtlessly follows the empty ceremonies of Catholic worship, is at once assumed to be a good citizen, even if there be no meaning whatever in his faith and his morality be deplorable. This error will only be destroyed when, in the twentieth century, the prevalent superstition gives place to rational knowledge and to a monistic conception of the unity of God and the world. CHAPTER XVI KNOWLEDGE AND BELIEF The Knowledge of the Truth and Its Sources: the Activity of the Senses and the Association of Presentations--Organs of Sense and Organs of Thought--Sense-Organs and their Specific Energy--Their Evolution--The Philosophy of Sensibility--Inestimable Value of the Senses--Limits of Sensitive Knowledge--Hypothesis and Faith--Theory and Faith--Essential Difference of Scientific (Natural) and Religious (Supernatural) Faith--Superstition of Savage and of Civilized Races--Confessions of Faith--Unsectarian Schools--The Faith of Our Fathers--Spiritism--Revelation Every effort of genuine science makes for a knowledge of the truth. Our only real and valuable knowledge is a knowledge of nature itself, and consists of presentations which correspond to external things. We are incompetent, it is true, to penetrate into the innermost nature of this real world--the "thing in itself"--but impartial critical observation and comparison inform us that, in the normal action of the brain and the organs of sense, the impressions received by them from the outer world are the same in all rational men, and that in the normal function of the organs of thought certain presentations are formed which are everywhere the same. These presentations we call _true_, and we are convinced that their content corresponds to the knowable aspect of things. We _know_ that these facts are not imaginary, but real.