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In parapsychology, psi (From the Greek, psi, twenty-third letter of the Greek alphabet; from the Greek psyche, “mind, soul”)[1] is a neutral term for parapsychological phenomena, such as extra-sensory perception (ESP) and psychokinesis (PK).[2] "Psi" is pronounced with a silent "p", i.e., like "si" in "silent".[3] The term was coined by biologist Benjamin P. Wiesner, and first used by psychologist Robert Thouless in a 1942 article published in the British Journal of Psychology.[4] Psi was argued by Thouless and Wiesner to offer a non-theoretical manner of referring to ESP and PK, these terms being unjustifiably loaded with suggestions as to how the phenomena were caused or experienced.

Although Thouless and Wiesner were careful to offer psi as merely referring to certain phenomena worthy of study, it has come to connote the processes that somehow cause these phenomena, or a certain faculty of human psychology. In a 1994 paper in the Psychological Bulletin, Daryl J. Bem and Charles Honorton defined psi thus:

The term psi denotes anomalous processes of information or energy transfer, processes such as telepathy or other forms of extrasensory perception that are currently unexplained in terms of known physical or biological mechanisms. The term is purely descriptive: It neither implies that such anomalous phenomena are paranormal nor connotes anything about their underlying mechanisms.[5]

Similarly, according to the Parapsychological Association, psi can be

used either as a noun or adjective to identify paranormal processes and paranormal causation; the two main categories of psi are psi-gamma (paranormal cognition; extrasensory perception and psi-kappa (paranormal action; psychokinesis), although the purpose of the term "psi" is to suggest that they might simply be different aspects of a single process, rather than distinct and essentially different processes.[6]

In popular culture, "psi phenomena" have become synonymous with psychic and "psionic" phenomena.

See also

  • Psi, for other meanings.
  • Parapsychology
  • Psionics
  • Extra Sensory Perception


  1. Parapsychological Association website, Glossary of Key Words Frequently Used in Parapsychology, Retrieved January 29, 2007
  2. What do parapsychologists study?, From the FAQ of the website of the Parapsychological Association, Retrieved February 3, 2007
  3. Retrieved February 5, 2007
  4. Thouless, R. H. (1942). Experiments on paranormal guessing. British Journal of Psychology, 33, 15-27.
  5. Bem, D. J., & Honorton, C. (1994). Does psi exist? Replicable evidence for an anomalous process of information transfer. Psychological Bulletin', 115, 4-18.
  6. Parapsychological Association Glossary of Parapsychological terms

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