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Clever Hans phenomenon

A form of involuntary and unconscious cuing. The term refers to a horse (Kluge Hans, referred to in the literature as "Clever Hans") who responded to questions requiring mathematical calculations by tapping his hoof. If asked by his master, William Von Osten, what is the sum of 3 plus 2, the horse would tap his hoof five times. It appeared the animal was responding to human language and was capable of grasping mathematical concepts. It was 1891 when Von Osten began showing Hans to the public. (Hans could also tell time and name people,* but we will restrict our discussion of his amazing abilities to his mathematical skills.) It was eventually discovered (in 1904) by Oskar Pfungst that the horse was responding to subtle physical cues (ideomotor reaction) or as Ray Hyman puts it "Hans was responding to a simple, involuntary postural adjustment by the questioner, which was his cue to start tapping, and an unconscious, almost imperceptible head movement, which was his cue to stop" (Hyman 1989: 425). Yet, more than a dozen scientists observed Hans and were convinced there was no signaling or trickery (Randi 1995: 49). They were impressed that Hans performed almost as well without Von Osten as with him (Schick and Vaughn 1988: 116). But the scientists were wrong.

The horse was simply a channel through which the information the questioner unwittingly put into the situation was fed back to the questioner. The fallacy involved treating the horse as the source of the message rather than as a channel through which the questioner's own message is reflected back (Hyman 1989: 425).

Pfungst noted that when the correct answer was not known to anyone present, Clever Hans didn't know it either. And when the horse couldn't see the person who did know the answer, the horse didn't respond correctly (Schick and Vaughn, loc. cit.). This led Pfungst to conclude that the horse was getting visual cues, albeit subtle ones. It turned out that Von Osten and others were cuing Hans unconsciously by "tensing their muscles until Hans produced" the correct answer (ibid.). The horse truly was clever, not because he understood human language but because he could perceive very subtle muscle movements. More important, Pfungst discovered that people can unconsciously communicate information to others by subtle movements and that some animals can perceive these unconscious movements. It was only a matter of time before psychologists would be investigating nonverbal influence among humans. (See Robert Rosenthal 1998.)

It is often the case that animals are thought to show evidence of linguistic abilities that they do not possess. And humans are thought to be capable of grasping psychic messages when they are just sensitive to the unconscious signaling of others.

Unconscious cuing has even led to the belief in the psychic abilities of animals. James Randi relates the story of J. B. Rhine who declared that the horse Lady Wonder was psychic because she could answer questions by knocking over alphabet blocks (Randi 1995: 143). In Rhine's opinion, there was no trickery involved. He concluded that the only tenable hypothesis for the horse's abilities was that the horse was telepathic. Rhine's first test of Lady Wonder was in 1927. When he returned two years later, Rhine determined that the horse had lost its telepathic abilities in the interim (Christopher 1970: 21). Rhine's reasoning is an example of the false dilemma fallacy.

See also clever Linda phenomenon, hidden persuaders, psychic animals, and A Short History of Psi Research by Robert Todd Carroll.

further reading

books and articles

Candland,  Douglas Keith. Feral Children and Clever Animals: Reflections on Human Nature (Oxford University Press 1995).

Christopher,Milbourne. ESP, Seers & Psychics (Thomas Y. Crowell Co. 1970).

Hyman, Ray. The Elusive Quarry: a Scientific Appraisal of Psychical Research (Buffalo, N.Y.: Prometheus Books, 1989).

Jay, Ricky. Learned Pigs & Fireproof Women (Farrar Straus & Giroux 1998).

Pfungst, Oskar. Clever Hans: The Horse of Mr Von Osten (Thoemmes Press 2000).

Randi, James. An Encyclopedia of Claims, Frauds, and Hoaxes of the Occult and Supernatural, (N.Y.: St. Martin's Press, 1995).

Rosenthal,Robert. 1998. "Covert Communication in Classrooms, Clinics, and Courtrooms," Eye on Psi Chi. Vol. 3, No. 1, pp. 18-22.

Sebeoke,  Thomas A. and Robert Rosenthal Sebeoke. editors. Clever Hans Phenomenon: Communication With Horses, Whales, and People (New York Academy of Sciences 1970).

Schick, Jr., Theodore and Lewis Vaughn, How to Think About Weird Things 3rd ed. (McGraw-Hill, 2001), 

Umiker-Sebeok, Jean, and Thomas A. Sebeok. 1981. Clever Hans and Smart Simians: The Self-Fulfilling Prophecy and Kindred Methodological Pitfalls. Anthropos 76:89-165.


Classics in Psychology Robert H. Wozniak - Bryn Mawr College Oskar Pfungst: Clever Hans (The Horse of Mr. von Osten) (1907; English 1911)

Clever Hans, the "Psychic" Horse by D. Trull

More on Monkey Talk by Jean Umiker-Sebeok, Thomas A. Sebeok New York Review of Books, Volume 27, Number 19, December 4, 1980.

Psychic pets and pet psychics by Joe Nickell


Handler beliefs affect scent detection dog outcomes I couldn't decide whether to link this story under Clever Hans or facilitated communication, so I'm placing it in both entries. It seems that sniffer dogs aren't doing the finding, their handlers are. At least that's what a study of 18 dogs and their human handlers found. The study is small and didn't use drugs or explosives. Next step?

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