The field of psychical research must be unique in one respect at least: no other discipline, so far as I know, has its subject-matter demarcated by exclusively negative criteria. A phenomenon is, by definition, paranormal if and only if it contravenes some fundamental and well-founded assumption of science. This alone is what makes it of interest to this Society.
Now, one would need to be almost perversely fond of mystification to sustain an interest in anything for any length of time for no other reason than that it was odd and inexplicable. Most psychical researchers, I feel sure, are drawn to their pursuit because they intuitively feel that these phenomena represent an important riddle about the nature of things which they want to decipher. Of course, there can be no logical guarantee that paranormal phenomena will turn out to possess anything in common beyond their negative qualifications, but there is plenty of precedent for trying to find some overall guiding principle which might embrace at least the major phenomena. In this talk I want, therefore, to discuss what such a guiding principle might be. Now, there are, on my reckoning, no more than five possibilities that are still seriously worth considering. I propose, therefore, to describe briefly each of them in turn and then weigh their respective claims on our allegiance.
The first of these basic positions which immediately confronts every
Reprinted from the Journal of the Society for Psychical Research, volume 42 ( 1963), pp. 101- 114, by permission of the author and editor.