It is the oldest fear about hypnosis: that someone could be turned into an instrument, made to steal or kill, and remember nothing. Novels and films have used it for well over a century. Courts have occasionally believed it. And for a time, laboratory experiments appeared to prove it.
Then one researcher added a control group, and the picture changed.
The Copenhagen case
On 29 March 1951, a man named Palle Hardrup walked into a bank in Copenhagen, attempted a robbery, and shot dead two bank employees.
His defence was extraordinary. He said he had acted under the hypnotic influence of another man, Bjørn Schouw Nielsen, whom he had met in prison, and who had spent years establishing control over him.
The court accepted it. It found that Nielsen had hypnotized the 28-year-old Hardrup to carry out the robbery and the killings, and the Danish Supreme Court upheld the decision. Both men were convicted and imprisoned, and both were released in 1967.
The case remains controversial. Hardrup later retracted his account. Critics argue that the relationship was one of long-term domination and manipulation, of a kind that needs no hypnosis to explain it.
The early experiments
In 1939 an American psychologist, Loyd Rowland, reported a startling study. Deeply hypnotized subjects were asked to reach for a large rattlesnake, and to throw acid at an experimenter’s face. Most tried to. (Invisible glass protected everyone.)
In 1952 another researcher repeated it with similar results. Hypnotized subjects reached into a beaker of fuming nitric acid to retrieve a coin, picked up a venomous snake, and threw the acid at an assistant.
It looked like proof that hypnosis could compel people to do dangerous and harmful things.
Orne’s control group
In the 1960s the psychiatrist Martin Orne, with Frederick Evans, repeated the experiments with one addition. Alongside the hypnotized subjects he included simulators: people who were not hypnotized, and who had been asked to pretend to be, in order to fool the experimenter.
The simulators did everything the hypnotized subjects did. In fact they were, if anything, more likely to carry out the “dangerous” acts. Further groups who were simply asked to do the tasks as part of an experiment also complied at high rates.
Afterwards, participants explained why. They knew they were in a university laboratory. They assumed, correctly, that a responsible scientist would not let anyone get hurt. The situation was not really dangerous, and they knew it.
Orne’s conclusion was direct: the popular view that hypnosis exerts a unique form of control, able to compel a person to carry out otherwise repugnant actions, must be rejected.
What this shows
People in the earlier experiments had not been overpowered by hypnosis. They had been responding to the situation: an authority figure, a scientific setting, and an implicit guarantee of safety.
Orne called these pressures demand characteristics. The same forces were at work in Stanley Milgram’s obedience experiments of the same era, in which ordinary people delivered what they believed were severe electric shocks because a man in a lab coat told them to. No hypnosis was involved.
So the uncomfortable truth is not that hypnosis can make people do terrible things. It is that people will do a great deal when a trusted authority asks them to, with or without it.
Could a hypnotist deceive someone?
This is the more subtle question. Suppose the hypnotist does not ask for something the person finds wrong, but changes how the situation appears: “This is a toy gun.” “That man is about to attack your child.”
In principle a person can be deceived into harmful action. But that is true without hypnosis as well. Con artists and abusers manage it with words alone, and research has not shown that hypnosis adds any special power.
The real risks
The danger in hypnosis is not mind control. It is ordinary abuse of a position of trust.
- A practitioner may exploit a client financially, emotionally or sexually. Such cases have occurred and been prosecuted.
- Hypnosis may be used as cover for deception.
- A vulnerable person may be led over time into dependence.
These are the risks of any relationship involving trust and authority. The remedies are the same: qualified, accountable practitioners, clear boundaries, and the right to stop at any moment.
And as a defence?
“I was hypnotized” almost never succeeds in court. Legal systems generally treat a person as responsible for their actions, and the scientific consensus gives no support to the idea of an irresistible hypnotic command. The Copenhagen verdict is remembered because it is so unusual.
What about stage shows?
Volunteers do embarrassing things because they have chosen to be part of a performance, in front of a crowd, with a ready-made excuse. It is social pressure and permission, the same forces Orne identified.
What you can take from this
- You keep your values under hypnosis.
- You can refuse a suggestion, and people do.
- You can open your eyes and stop.
- No good evidence shows that hypnosis can compel anyone to act against their will.
- The risk worth guarding against is an untrustworthy practitioner, not a loss of control.
The bottom line
The belief that hypnosis can turn people into puppets was undone by a control group. People who were only pretending to be hypnotized behaved the same way. What moves people to act is trust, authority and their reading of the situation. That is a more sobering lesson than the myth it replaced.
Next in the series: Hypnosis and Religion: Is It Compatible With Your Faith?
This article is for general information and is not legal advice.