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 recent 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.
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)