Clever Hans, the counting horse

We, the children, knew it. On the night of the Epiphany, animals could talk. But nobody was allowed to listen to them. If an unfortunate person had overheard their words, he should have expected decades of troubles. Anyway, to make sure they didn’t say anything wrong about them, on the night of 5 January, the elders of my village cooked a special meal for their dogs, cats, or chickens.

Thinking animals

We love the idea that animals can communicate with us. We find speaking or thinking animals in many legends or fairy tales. In recent years, scientists deepened their knowledge of animal intelligence, and today we have a better understanding of it. For example, we know many species have complex ways to communicate with each other and that some animals can count. For example, fish, frogs, wolves, monkeys, and chickens do it. Cats, on the other hand… Well, we don’t know much about cats. Anyone who lives with one of these cute felines knows how difficult it is to convince them to do anything. Despite many attempts to study their intellectual abilities, cats have consistently shown that they are not interested in stupid tests. As already noticed, a hundred years ago, the German teacher Wilhelm von Osten.

Hans goes to school

Convinced that animals had human-like abilities, Von Osten miserably failed when he tried to demonstrate it by training a cat. He didn’t do very well with bears either and only concluded that these big mammals can be pretty hostile when a human annoys them. So he fell back on Hans, a tame Orlov horse with whom he had established an empathic relationship. After four years of daily training with a giant abacus and some cards reproducing the letters of the alphabet, Von Osten’s four-legged pupil was ready. Scientists and onlookers gathered in the courtyard of a school in Berlin where the teacher showed up with long hair, an uncombed beard, a loose tunic and a floppy hat. But the audience took no notice. The focus was all on Hans’ extraordinary abilities.

The thinking horse

Bystanders submitted to the horse several mathematical problems. Hans answered each question by tapping his hoof, demonstrating its ability to solve additions, subtractions, and square roots. Similarly, it could identify the letters of the alphabet, colours and musical notes.

On July 7, 1904, an article in the German newspaper Weltspiegel celebrated the extraordinary abilities of the animal. Many declared to have become emotional for its special intellectual faculties. Others claimed the horse was under a mesmeric influence. Esotericist Rudolf Steiner argued Von Osten could use telepathy to communicate the correct answers to the horse. However, there was no shortage of detractors who believed it was just a scam. Those statements intensely annoyed Von Osten, who was sure to have always acted correctly. To silence any doubts, the professor said he was willing to have the horse examined by a scientific committee.

No trick, no deception

On September 11, 1904, Hans was taken before the director of the Psychology Institute of Berlin, a zoologist, a veterinarian, several cavalry officers and Paul Busch, whose career as a circus director elevated him as an expert of equine communication. The horse was tested for two days, after which the commission concluded that there was no fraud. On the contrary, the experts asserted (albeit cautiously) that Hans was endowed with genuine intellectual faculties.

Rather than silencing Von Osten’s detractors, the dispute escalated. Many scientists became convinced that animals could express themselves in a human-like language, just as fairy tales and legends have claimed for a long time. Others accused the experts of doing their job superficially. Once again, Von Osten agreed to subject Hans to a new examination.

A young man named Oskar Pfungst

The Psychology Institute of Berlin assigned the case of the world’s most intelligent horse to a young scholar named Oskar Pfungst. He began his investigation by following the same method as his colleagues. For each correct answer, he rewarded Hans with a piece of bread, a carrot or a lump of sugar. Hans proved himself exceptionally gifted and scored 98% correct answers, even when Von Osten was made to leave the room to dispel any doubt of secret communication between the horse and its owner. If there was a trick, it had to be elsewhere.

For this reason, the psychologist did something that no one before him had tried, and the percentage of correct answers dropped to 6%. In practice, the horse could only guess by chance. What had happened? Pfungst had subjected Hans to a blind experiment, an evaluation technique already known but still unusual in the scientific practice. If the person asking did not know the answer or was outside Hans’ field of vision, the horse was wrong. Von Osten wasn’t the one cheating. Everyone did.

Clever Hans, or how (not) to carry out a scientific experiment

Just like the horse wished to be gratified with a piece of bread or a carrot, scientists also subconsciously aimed for their reward: the certainty they were dealing with a thinking animal. The examiners imperceptibly changed their expression or made an involuntary gesture when the horse tapped its hoof a number of times equal to the correct answer. Hans just had the ability to pick up on those unconscious signals. This case demonstrated how easy it is to unintentionally manipulate a study subject to get the desired results. The international scientific community realized that blind experiments had to become the rule.

The end of Clever Hans

To our knowledge, Von Osten did not accept Pfungst’s conclusions and held a grudge against the psychologist throughout his life. But he did not blame Hans. The teacher kept the horse with him until his death. Then it was sold. We don’t know exactly to whom. Some say to a barker who put it on shows with “thinking animals,” fooling unsuspecting paying spectators. But the most interesting story tells that Hans was purchased by the German army and used as a military horse during WWI. At his death, which occurred on the battlefield, it received no commendation for its service to the country and science but was eaten by soldiers left without food supplies.

To know more:

• Harry Miles Johson. «A Review of Clever Hans (the Horse of Mr. von Osten)». The Journal of Philosophy, Psychology and Scientific Methods, Nov. 23, 1911, Vol. 8, №24, pp. 663–666, 2021.
• Heini K.P. Hediger. «The Clever Hans Phenomenon from an Animal Psychologist’s Point of View». Annals of the New York Academy of Sciences 364, n. 1 (1981): 1–17.
• Laasya Samhita e Hans J Gross. «The “Clever Hans Phenomenon” Revisited». Communicative & Integrative Biology 6, n. 6 (November 9, 2013).
• Oskar Pfungst e Carl Leo Rahn. Clever Hans (the Horse of Mr. Von Osten) a Contribution to Experimental Animal and Human Psychology. New York, H. Holt and company, 1911.
• Richard Wiseman. Paranormality: The Science of the Supernatural. Pan Books, 2015.
• Rudolf Steiner. Bees. SteinerBooks, 1998.
• Vinciane Despret, Brett Buchanan, Bruno Latour. What Would Animals Say If We Asked the Right Questions? Posthumanities 38. Minneapolis: University of Minnesota Press, 2016.