“Telepathy and Other Untestable Hypotheses”, 1974-06 (; backlinks):
The hypothesis of telepathy as a mind-to-mind transference of thought from one person to another has not, even after a century of effort, been found to be verifiable. Unlike the other subtypes of psi ability (clairvoyance, precognition, and psychokinesis), it has not been possible to design a definitive experimental test of telepathy. A review is given here of the history of the main attempts to solve this problem and the evident failure to do so.
Attention is directed to the reason for this unprofitable outcome, and the suggestion is made that telepathy be indefinitely shelved until, if ever, a conclusive test design is discovered.
A number of other hypotheses that are currently investigated are similarly quite untestable by any known design that could lead to conclusive results. The other problems discussed here are: spirit projection (out-of-the-body experiences), spirit communication of various types, and retroactive psi (such as retrocognition or “psychometry” and retroactive PK).
The author’s aim is to get parapsychology out of its long and wasted preoccupation with unsolvable questions without necessarily dismissing them with finality.