Now people at all times have been commanded or expected or invited to accept on authority alone—the authority, for instance, of public opinion, or a Church, or a sacred book—doctrines which are not proved or are not capable of proof. Most beliefs about nature and man, which were not founded on scientific observation, have served directly or indirectly religious and social interests, and hence they have been protected by force against the criticisms of persons who have the inconvenient habit of using their reason. Nobody minds if his neighbour disbelieves a demonstrable fact. If a sceptic denies that Napoleon existed, or that water is composed of oxygen and hydrogen, he causes amusement or ridicule. But if he denies doctrines which cannot be demonstrated, such as the existence of a personal God or the immortality of the soul, he incurs serious disapprobation and at one time he might have been put to death. Our mediaeval friend would have only been called a fool if he doubted the existence of Constantinople, but if he had questioned the significance of comets he [18] might have got into trouble. It is possible that if he had been so mad as to deny the existence of Jerusalem he would not have escaped with ridicule, for Jerusalem is mentioned in the Bible. In the Middle Ages a large field was covered by beliefs which authority claimed to impose as true, and reason was warned off the ground. But reason cannot recognize arbitrary prohibitions or barriers, without being untrue to herself. The universe of experience is her province, and as its parts are all linked together and interdependent, it is impossible for her to recognize any territory on which she may not tread, or to surrender any of her rights to an authority whose credentials she has not examined and approved. The uncompromising assertion by reason of her absolute rights throughout the whole domain of thought is termed rationalism, and the slight stigma which is still attached to the word reflects the bitterness of the struggle between reason and the forces arrayed against her. The term is limited to the field of theology, because it was in that field that the self-assertion of reason was most violently and pertinaciously opposed. In the same way free thought, the refusal of thought to be controlled by any authority but its own, has a definitely theological reference. Throughout