In this book we propose to study the most primitive and simple religion which is actually known, to make an analysis of it, and to attempt an explanation of it. A religious system may be said to be the most primitive which we can observe when it fulfils the two following conditions: in the first place, when it is found in a society whose organization is surpassed by no others in simplicity; and secondly, when it is possible to explain it without making use of any element borrowed from a previous religion.We shall set ourselves to describe the organization of this system with all the exactness and fidelity that an ethnographer or an historian could give it. But our task will not be limited to that: sociology raises other problems than history or ethnography. It does not seek to know the passed forms of civilization with the sole end of knowing them and reconstructing them. But rather, like every positive science, it has as its object the explanation of some actual reality which is near to us, and which consequently is capable of affecting our ideas and our acts: this reality is man, and more precisely, the man of to-day, for there is nothing which we are more interested in knowing. Then we are not going to study a very archaic religion simply for the pleasure of telling its peculiarities and its singularities. If we have taken it as the subject of our research, it is because it has seemed to us better adapted than any other to lead to an understanding of the religious nature of man, that is to say, to show us an essential and permanent aspect of humanity.