Clever Hans – The Horse who could do Arithmetic


“Clever Hans” was an Orlov Trotter horse that was claimed to have been able to perform arithmetic and other intellectual tasks.

After a formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was not actually performing these mental tasks, but was watching the reactions of his human observers. Pfungst discovered this artifact in the research methodology, wherein the horse was responding directly to involuntary cues in the body language of the human trainer, who had the faculties to solve each problem. The trainer was entirely unaware that he was providing such cues. In honour of Pfungst’s study, the anomalous artifact has since been referred to as the “Clever Hans effect” and has continued to be important knowledge in the observer-expectancy effect and later studies in animal cognition. Hans was studied by the famous German philosopher and psychologist Carl Stumpf in the early 20th century. Stumpf was observing the sensational phenomena of the horse, which also added to his impact on phenomenology.

During the early twentieth century, the public was especially interested in animal intelligence owing in a large part to Charles Darwin’s then-recent publications.

Hans was a horse owned by Wilhelm von Osten, who was a gymnasium mathematics teacher, an amateur horse trainer, phrenologist, and something of a mystic.
Hans was said to have been taught to add, subtract, multiply, divide, work with fractions, tell time, keep track of the calendar, differentiate musical tones, and read, spell, and understand German. Von Osten would ask Hans, “If the eighth day of the month comes on a Tuesday, what is the date of the following Friday?” Hans would answer by tapping his hoof. Questions could be asked both orally, and in written form. Von Osten exhibited Hans throughout Germany, and never charged admission. Hans’s abilities were reported in “The New York Times” in 1904. After von Osten died in 1909, Hans was acquired by several owners. After 1916, there is no record of him and his fate remains unknown.

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