The argument pursued in these pages is based, substantially, not on theories of Christian development to which it has been sought to bring the literary data into conformity, but on a direct application to those data of general principles of comparative documentary criticism. It may be worth while to state some of those principles in their generalized form:

1. Where two or more documents correspond in contents, order and language beyond the degree that is necessitated by their subject or probably explicable by accidental coincidence, there is a presumption that, unless inter-dependent, they share (immediately or mediately) a common written or oral source.

2. Where these correspondences or identities attain a certain degree of minuteness the balance is tilted against the hypothesis of merely oral connection.

3. Unless external considerations urge, it is unscientific to conjecture hypothetical documents to explain correspondences for which a theory of direct inter-dependence is sufficient.

4. In determining the direction of dependence (i.e. whether document A depends on document B, or vice versa) weight must be given to the internal coherence of subject-matter on the one hand, and to the employment of merely external links in combining material on the other hand. We may also be helped by a knowledge of the literary methods and the psychology of one or both authors, and especially by evidence of an author's deviation from his habitual style or vocabulary under the influence of a source.

Iceland, that island of marvels, has preserved for us, as it has done in most other fields of Germanic culture, nearly all of what we know about the religion of our pagan ancestors. The two Eddas, the Elder (Poetic) and the Younger (Prose) Edda, furnish the whole body of coherent mythology accessible to us. As for the cults themselves, we are much less well informed, but such knowledge as we have is drawn mainly from the Sagas, prose tales dealing with men and events, real and fictitious, of the heathen time, written down two or three centuries after the adoption of Christianity as the state religion in the year 1000, yet seeking to give a faithful picture of the manners and beliefs of the old days, and with scarcely a trace of the intolerance which almost obliterated the pagan traditions in other parts of Germanic territory. The distribution and popularity of the cults, their relative age and gradual expansion have been revealed by the brilliant researches of Professor Magnus Olsen on the Norwegian place-names and by the subsequent studies inspired by his work.