Suggestion

Suggestion is the psychological process by which a person guides their own thoughts, feelings, behaviours or bodily states, or those of another person, by presenting stimuli that tend to evoke them as reflexes rather than through conscious effort. The word, common in everyday speech, took on a technical meaning in nineteenth-century psychology. William James used "suggest" to describe an idea that brought another idea to mind, and the early scientific studies of hypnosis by Clark Leonard Hull and others extended that sense until it became a subject of experimental research. The first neuropsychological account of hypnotic suggestion relied on the ideomotor reflex that William B. Carpenter proposed in 1852 to explain the phenomena James Braid had attributed to hypnotism.

In the therapeutic field, Émile Coué was one of the pioneers in understanding suggestion as a tool for treatment. His method aimed to saturate the cognitive environment of the mind with positive suggestions. He held that these could produce bodily effects, that specific suggestions led to specific outcomes, and that they worked as well for physical complaints as for emotional ones, without implying that the original complaint was imaginary. Charles Baudouin later formulated several "laws of suggestion", among them the law of concentrated attention, by which an idea on which spontaneous attention is fixed tends to become real, and the law of reversed effort, by which imagination wins when conscious will conflicts with it.

Modern scientific hypnosis distinguishes two elements: the trance, induced through instructions, and the suggestion itself. To measure suggestibility, researchers use suggestions such as that an arm is growing lighter and rising into the air. Nevertheless, the work of Nicholas Spanos and Irving Kirsch found a strong correlation between responses to suggestion inside and outside hypnosis, leading some authors to see suggestibility as a broader trait rather than a phenomenon limited to trance.

Today the concept is debated between those who regard it as a key element of therapy, education and advertising, and those who warn of its power to shape beliefs without the person noticing. It remains central to psychology, psychosomatic medicine and the study of eyewitness testimony.