The central theoretical disagreement is known as the "state versus nonstate" debate. When Braid introduced the concept of hypnotism he equivocated over the nature of the "state", sometimes describing it as a specific sleep-like neurological state comparable to animal hibernation or yogic meditation, while at other times he emphasised that hypnotism encompassed a number of different stages or states which were an extension of ordinary psychological and physiological processes. Overall, Braid appears to have moved from a more "special state" understanding of hypnotism toward a more complex "nonstate" orientation. State theorists interpret the effects of hypnotism as primarily due to a specific, abnormal and uniform psychological or physiological state of some description, often referred to as "hypnotic trance" or an "altered state of consciousness." Nonstate theorists rejected the idea of hypnotic trance and interpret the effects of hypnotism as due to a combination of multiple task-specific factors derived from normal cognitive, behavioural and social psychology, such as social role-perception and favorable motivation (Sarbin), active imagination and positive cognitive set (Barber), response expectancy (Kirsch), and the active use of task-specific subjective strategies (Spanos). The personality psychologist Robert White is often cited as providing one of the first nonstate definitions of hypnosis in a 1941 article:
Hypnotic behaviour is meaningful, goal-directed striving, its most general goal being to behave like a hypnotised person as this is continuously defined by the operator and understood by the client.
Put simply, it is often claimed that whereas the older "special state" interpretation emphasises the difference between hypnosis and ordinary psychological processes, the "nonstate" interpretation emphasises their similarity.
Comparisons between hypnotised and non-hypnotised subjects suggest that if a "hypnotic trance" does exist it only accounts for a small proportion of the effects attributed to hypnotic suggestion, most of which can be replicated without hypnotic induction.