The revolution by which piety and worship were relegated to the private sphere is often attributed to the rise of personal conscience and assertion of its rights. But this rise is just the thing to be accounted for. The supposition that it was there all the time in a submerged condition and finally dared to show itself reverses the order of events. Social changes, both intellectual and in the internal composition and external relations of peoples, took place so that men no longer connected attitudes of reverence or disrespect to the gods with the weal and woe of the community. Faith and unbelief still had serious consequences, but these were now thought to be confined to the temporal and eternal happiness of the persons directly concerned. Given the other belief, and persecution and intolerance are as justifiable as is organized hostility to any crime; impiety is the most dangerous of all threats to public peace and well-being. But social changes gradually effected as one of the new functions of the life of the community the rights of private conscience and creed. In general, behavior in intellectual matters has moved from the public to the private realm. This radical change was, of course, urged and justified on the ground of intrinsic and sacred private right. But, as in the special case of religious beliefs, it is strange, if this reason be accepted, that mankind lived so long in total unawareness of the existence of the right. In fact, the idea of a purely private area of consciousness, where whatever goes on has no external consequences, was in the first instance a product of institutional change, political and ecclesiastic, although, like other beliefs, once it was established it had political results. The observation that the interests of the community are better cared for when there is permitted a large measure of personal judgment and choice in the formation of intellectual conclusions, is an observation which could hardly have been made until social mobility and heterogeneity had brought about initiation and invention in technological matters and industry, and until secular pursuits had become formidable rivals to church and state. Even yet, however, toleration in matters of judgment and belief is largely a negative matter. We agree to leave one another alone (within limits) more from recognition of evil consequences which have resulted from the opposite course rather than from any profound belief in its positive social beneficence. As long as the latter consequence is not widely perceived, the so-called natural right to private judgment will remain a somewhat precarious rationalization of the moderate amount of toleration which has come into being. Such phenomena as the Ku Klux and legislative activity to regulate science show that the belief in liberty of thought is still superficial.