The foregoing pages constitute an attempt to answer this question. The need for some such investigation was clearly shown by the publication of the late Professor William James's _Varieties of Religious Experience_ and its reception by the religious press of the country as an epoch-marking work. As a mere collection of documents, the work is interesting enough. But its critical value is extremely small. How religious visionaries have felt, or what has been their experiences, can only furnish the mere data of an enquiry, and _their explanation of the cause of their experiences is a part of the data_. This, apparently, Professor James overlooked; and it will be noted by critical readers of his book that it proceeds on the assumption that the statements of religious visionaries are to be taken, not only as true concerning their subjective experiences at a given time, but also as approximately true as to the causes of their mental states. This, of course, by no means follows. A scientific enquiry cannot separate mental conditions from the subject's interpretation of their causation. Whether this interpretation is genuine or not must be decided finally by an appeal to what is known of the laws of mental life, under both normal and abnormal conditions. If these are adequate to explain the "Varieties of Religious Experience," there is no need whatever to assume the operation of a supernatural agency. Nor does calling this agency 'transcendent' or 'supermundane' make any substantial difference. For, in this connection, these are only names that serve to disguise a visitant of a highly undesirable character.