The debate about how to define 'hypnotizability' goes to the heart of what hypnosis is. The way we define hypnotizability affects how we use hypnosis clinically, and it affects the kinds of experiments that we do to investigate what hypnosis is and how it can be used. A consensus paper by Kirsch and colleagues, stemming from a discussion at the 2006 BSCAH conference, outlined the implications of two different definitions of hypnotizability. The positions are outlined below.


Broad DefinitionNarrow Definition

Hypnotizability = suggestibility following a hypnotic induction

Hypnotizability = changes in suggestibility brought about by the induction of hypnosis

Retains the traditional use of 'hypnotizability' to denote what is measured by scales

Consistent with the 'generally accepted approach to hypnosis research': "no behaviour following hypnotic induction can be attributed to hypnosis unless the investigator first knows that the response in question is not likely to occur outside of hypnosis in the normal waking state" (Sheehan & Perry, 1975, p55)

We can no longer say that hypnosis enhances suggestibility because responsing to suggestion is the definition of hypnosis

Have to reconceptualize what we mean by hypnotizability - need to measure suggestibility with and without hypnotic induction

Avoids problem of 'negative hypnotizability' (people who respond more strongly to waking suggestions than to hypnotic suggestions

Renders 'hypnosis' a concept of fairly limited utility, since most interesting phenomena can be brought about by suggestion alone


The 2014 APA definition of hypnosis used the broad definition of hypnotizability.

“An individual’s ability to experience suggested alterations in physiology, sensations, emotions, thoughts, or behavior during hypnosis.” (APA, 2014)

The APA's was a political decision - based in part upon the opinions of a survey of members who are a mix of clinicians and researchers. My opinion is that the narrow definition is the logical choice from the point of view of research becuase it demands clearer specification of what one did. The broad definition makes assumptions about when a person is hypnotized - essentially if they respond to suggestions they are said to be hypnotized.

Controversy about definitions of hypnotizability

The debate about how to define hypnotizability can get quite polarised:

"If we were to accept the rationale of the Kirsch and Braffman method [the narrow definition], this would mean that the question of a 'hypnotic effect' then pivots on 'Does using the word "hypnosis" in the protocol make a difference to how people respond to subsequent suggestions over and beyond how they respond when the word 'hypnosis' is not mentioned'. This is a context question of modest interest ... The problem with these types of constricted definitions is that they drain the science of its relevance." (Barnier & Nash, 2008, pp 9-10)

Milling and colleagues (2010) note that conceptualising hypnotizability as the change in suggestibility following a hypnotic induction has been termed 'novel' by some researchers (e.g. Hutchinson-Philips et al, 2007). However, Kirsch, Mazzoni, & Montgommery (2007) note that it may be the original way of defining suggestibility, quoting Clark Hull:

"The essence of hypnosis lies in the fact of change in suggestibility" (Hull, 1933, pp.391)



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