What is Hypnosis?

Put three hypnotists in a room and ask them to define hypnosis — you’ll end up with four definitions and a dead hypnotist.

— Undine de Rivière
Interview with Cosmic Pancakes

To do hypnosis, it helps to understand what hypnosis does and how it works. Understanding the psychological underpinnings explains why so much emphasis goes into pre-talk and negotiation, and why inductions are structured the way they are.

The problem arises when you find that different people refer to hypnosis in different ways to refer to different concepts. There is no common definition for hypnosis, and different groups mean different things.

I’m going to attempt to square the circle and provide a definition which will be "good enough" at the cost of leaning very heavily on the surrounding context.

Questions

Consider the following questions.

Your friend joins a stage hypnosis show, and appears to be completely hypnotized. Afterwards, he says he was fully conscious and just playing along. Was he hypnotized?
A hypnotist talks about how he does not use hypnosis in his shows because he does not use inductions or tell people to go into a hypnotic state. Is he right?
You and your friends agree to play a game of Simon Says, and you are the first to get caught out. Afterwards, one of your friends says you were hypnotized. Are they right?
You’re driving for a long period of time and arrive at your destination. Afterwards, you can’t quite remember what you were doing or thinking. Your friend says you had highway hypnosis. Were you really hypnotized?
Your partner sometimes talks in her sleep, and you’ve found she can talk to you without waking up. One night, you tell her she should make you coffee in the morning. She does, but has no memory of you telling her that. Was she hypnotized?
Derren Brown walks up to a stranger and tells her that her feet are stuck. Is she hypnotized?
Michael Fine, a divorce attorney, is convicted of hypnotizing his clients. Were they really hypnotized?
A youtube video shows a woman apparently being hypnotized and succumbing a progressive muscle relaxation induction against her will. Was she really hypnotized?
A friend says that she is trying out self-hypnosis by listening to youtube videos while she sleeps. Is that really hypnosis?
A study attempts to prove whether people were hypnotized with neuroimaging. Is it accurate?

Terms

We can define some terms up front and use these definitions to answer the above questions.

First, let’s start with what a hypnotic suggestion is.

Hypnotic Suggestion: a suggestion to perform an action or response that involves phenomenological control (control over perception) and may be attributed to automatic or nonviolitional behavior.

Unlike a normal suggestion, a hypnotic suggestion can lead to a feeling that the action being performed happens outside of the control of the hypnotee, either because the action happened before they intended to perform it, or because they felt "out of the loop" when the behavior was performed.

From here, we can define suggestibility.

Suggestibility: the quality of being inclined to accept and act on hypnotic suggestions.

We have to refine this a bit, because we want to distinguish hypnotic suggestibility from other kinds of suggestibility, like Simon Says. To do this, we add the idea of a social context where giving hypnotic suggestions is appropriate, i.e. a hypnotic context.

Context: a social expectation to assume the roles of hypnotist and hypnotee and give or follow suggestions, respectively.

Researchers say that the feeling of involuntary action is the "classic suggestion effect" with the implication that the perception of sense of agency is the most important thing about hypnosis. But to me, the most important thing about hypnosis is the context. Hypnosis is the establishment of and commitment to a hypnotic context: a framework in which one person agrees to follow appropriate suggestions involving alterations of perception and cognition. In no other circumstance will someone tell you to feel your hand stuck to the table or tell you to forget the number four and expect you to actually do that.

A hypnotic context does not have to be explicit; if you say you’re a hypnotist and ask someone if they want to have a fun experience, that is implicitly setting up the context. The context controls what kinds of suggestions you can make; in a hypnotic context you can ask people to imagine that their arm is stiff and they cannot bend it, but that is not a valid suggestion in a Simon Says context.

Realistically, this is still a simplification because there isn’t just one hypnotic context. The expectations for suggestions and appropriate behavior vary depending on social situation. Experimental and clinical hypnosis are very different, with clinical hypnosis tailored to the patient, and experimental hypnosis tailored to the experiment. Waking hypnosis may not involve a "trance" state or induction. "Active-alert" hypnosis involves a focused trance state during exercise. The entertainment of stage hypnosis in front of an audience is different from the relaxed play of recreational hypnosis with friends at home. Erotic hypnosis can range all the way from romantic to objectification. And non-consensual hypnosis is rare, but does exist. Each of these situations has a different hypnotic context.

It’s also important to make a distinction between hypnosis, relaxation, and trance. Waking hypnosis does not involve a trance state, and active-alert hypnosis does involve trance, but does not involve relaxation. If we consider waking hypnosis and alert-active hypnosis to be valid examples of hypnosis, then whatever trance is, it is not relaxation or hypnosis itself. Hypnosis and trance are commonly conflated, to the point where the myth of trance is described as the most pervasive misconception about hypnosis. What we can say about trance is that it is an altered state of consciousness associated with hypnosis. An altered state of consciousness is a multi-dimensional change in patterns of thought from consciousness judged as subjectively "baseline" or normal. Broadly speaking, it’s a subjective experience or internal feeling.

Using suggestibility and a hypnotic context, we can define the following terms in this model.

Hypnosis is suggestibility in a hypnotic context.
Hypnotic phenomena are responses in a hypnotic context.
A hypnosis session is a series of actions with the intent of producing hypnotic phenomena.
The act of hypnosis (or hypnotism) is a ritual establishing a hypnosis session.
Trance is a subjective feeling of hypnosis.

Using this definition, as soon as the hypnotic context is established and the hypnotee starts following suggestions (or even trying to follow them), they are suggestible in a hypnotic context and therefore in hypnosis. It does not matter whether the response feels voluntary or irresistible; in fact, a range of experiences is normal and can vary even within the same session. The hypnotee does not need to feel like they are in a trance, because the subjective feeling of being hypnotized is not required for suggestibility to exist.

Using these terms, hypnosis is not defined as increased suggestibility following an induction. While hypnosis can increase suggestibility, increased suggestibility is not required for hypnosis, and an induction is not required for hypnosis. All that’s required is a hypnotic context.

This is enough to answer the questions.

Answers

Conscious During Stage Hypnosis: your friend was hypnotized at the stage hypnosis show, because he agreed to a hypnotic context by getting up on stage and following suggestions.
Suggestions without Induction: the hypnotist is using hypnosis in his shows, because he refers to himself as a hypnotist and is implicitly defining a hypnotic context.
Simon Says: Playing Simon Says can increase suggestibility, but does not establish a hypnotic context, so you’re not hypnotized.
Hypnotized while Driving: "Highway hypnosis" is focused attention, not hypnosis.
Post-hypnotic suggestions: there is implicit memory during sleep, but there is no hypnotic context (no agreement to follow hypnotic suggestions). While hypnosis can feel like a dream-like state and can include amnesia, it’s most likely that your partner just likes you enough to bring you coffee.
Derren Brown ordering stuck: assuming that Derren Brown was not recognized as a hypnotist, this is raw suggestibility and not hypnosis.
Michael Fine: yes, the women were hypnotized. A hypnotic context was established, but his clients were told they were being led through breathing exercises, technically enough to establish it as co-operative.
Fighting Progressive Muscle Relaxation: Yes, this is hypnosis. She did not give consent, but she recognized the hypnotic context and the associated expectations and her reaction makes it clear that it was effective.
Hypnosis during sleep: Probably not. There are cases where simple motor function suggestions have worked during sleep, but hypnosis generally requires conscious attention.
Neuroimaging: There’s still no way to tell looking at a single person whether they’re "truly" hypnotized or not from neuroimaging. Studies can show that there’s brain activity, but it still must be interpreted by humans, and the findings are in conflict. One reason is that neuroscience does not have the tools to describe cognition, but another reason is that neuroimaging relies on statistical methods that can be easily misapplied to show meaning in noise, and so many studies have more in common with rorschach tests or tarot card readings than they do to actual results.