The Comparative Method notes the similarities and differences between the religions of different tribes or groups, and, gradually extending its field to embrace the whole species, endeavors, by excluding what is local or temporal, to define those forms of religious thought and expression which are common to humanity at large.
The Psychologic Method takes the results of both the previous methods and aims to explain them by referring the local manifestations to the special mental traits of the tribe or group, and the universal features to equally universal characteristics of the human mind.
The last, the Psychologic Method, is the crown and completion of the quest; for every advanced student of religion will subscribe to the declaration of Professor Granger, that “all mythology and all history of beliefs must finally turn to psychology for their satisfactory elucidation.”[3] In other words, the laws of human thought can alone explain its own products.
And here I must mention a startling discovery, the most startling, it seems to me, of recent times. It is that these laws of human thought are frightfully rigid, are indeed automatic and inflexible. The human mind seems to be a machine; give it the same materials, and it will infallibly grind out the same product. So deeply impressed by this is an eminent modern writer that he lays it down as “a fundamental maxim of ethnology” that, “we do not think; thinking merely goes on within us.”[4]
These strange coincidences find their explanation in experimental psychology. This science, in its modern developments, establishes the fact that the origin of ideas is due to impressions on the nerves of sense. The five senses give rise to five classes of ideas, the most numerous of which are those from the sense of sight, visual ideas, and those from the sense of hearing, auditory ideas. The former yield the conceptions of space, motion, and lustre (colour, brightness, etc.), the latter that of time. From the sense of touch arise the “tactual” impressions, which yield the ideas of power and might, through the sensations of resistance and pressure, pleasure and pain. From these primary ideas (or perceptions), drawn directly from impressions, are derived secondary, abstract, and general ideas (apperceptions) by comparison and association (the laws of Identity, Diversity, and Similarity).