V. Claims which are absolutely disproved by deductive reasoning, and which therefore the special sciences to which they belong know to be false without any examination.
Among the more prominent of claims of this kind are those that relate to squaring the circle, flatness of the earth, perpetual motion, including "Keeley" and "Winter" motors, alchemy, astrology, "four dimensions of space," levitation, mind or thought reading, clairvoyance or second-sight, including prevision and retrovision.
To examine or discuss claims of this kind, for the purpose of determining their truth or falsity, is not only useless, but unscientific. In science there are three unpardonable sins—trusting the senses, non-experts attempting to do the work of experts, and using deduction for induction, or, vice versa, induction when only deduction should be used, as in the class of claims here under consideration.
The reconstructed principles of evidence explain the following problems in psychology, to which hitherto, so far as I know, no solution has been offered:
1. Why the logic of the schools has always been on the side of delusions.
For those who accept non-expert testimony science is the only delusion: everything is true except the truth. In the long discussion relating to various modern delusions between Mr. Wallace and Dr. Carpenter, Mr. Wallace, according to the rules of evidence, has throughout the best of the argument: his reasoning, for those who trust their senses, who believe that non-experts can do the work of experts, and who use induction when only deduction should be used, is unanswerable.
Likewise in all, or nearly all, the world's memorable contests between science and delusions, the truth has prevailed, not by virtue of logic, but in spite of it; the instincts of mankind—the one saving clause in the constitution of the human brain—rising up in their unconscious majesty, and vindicating their rights and their power against the tyranny of the senses and the cruelty of the syllogism. Logically, Copernicus and Galileo were wrong; and their accusers, backed by the concurring testimony of the eyes of all mankind through all the generations, have to this hour never been answered. Only on the side of error is there consistency; during all these recent days, when science sets its forces in array against any dominant delusion, as "animal magnetism," or "odic" force, or "psychic" force, or "spiritualism," it first closes its books of logic and forgets all the teachings of the university.
2. Why men of culture and genius, and especially of logical attainments, are more easily and profoundly deceived by delusions than men of ordinary ability.
The history of all delusions, so far as known, establishes the wisdom of the maxim of the father of modern conjurers—the famous Houdin: "It is easier to dupe a clever man than a fool." Jugglers, and illusionists,