But primitive religions do not merely aid us in disengaging the constituent elements of religion; they also have the great advantage that they facilitate the explanation of it. Since the facts there are simpler, the relations between them are more apparent. The reasons with which men account for their acts have not yet been elaborated and denatured by studied reflection; they are nearer and more closely related to the motives which have really determined these acts. In order to understand an hallucination perfectly, and give it its most appropriate treatment, a physician must know its original point of departure. Now this event is proportionately easier to find if he can observe it near its beginnings. The longer the disease is allowed to develop, the more it evades observation; that is because all sorts of interpretations have intervened as it advanced, which tend to force the original state into the background, and across which it is frequently difficult to find the initial one. Between a systematized hallucination and the first impressions which gave it birth, the distance is often considerable. It is the same thing with religious thought. In proportion as it progresses in history, the causes which called it into existence, though remaining active, are no longer perceived, except across a vast scheme of interpretations which quite transform them. Popular mythologies and subtile theologies have done their work: they have superimposed upon the primitive sentiments others which are quite different, and which, though holding to the first, of which they are an elaborated form, only allow their true nature to appear very imperfectly. The psychological gap between the cause and the effect, between the apparent cause and the effective cause, has become more considerable and more difficult for the mind to leap. The remainder of this book will be an illustration and a verification of this remark on method. It will be seen how, in the primitive religions, the religious fact still visibly carries the mark of its origins: it would have been well-nigh impossible to infer them merely from the study of the more developed religions.