Hynek and others argued that a claimed close encounter must occur within about 150 meters (500 ft) to greatly reduce or eliminate the possibility of misidentifying conventional aircraft or other known phenomena.
[14] Hynek's former associate Jacques Vallée argued in the Journal of Scientific Exploration that the fourth kind should refer to "cases when witnesses experienced a transformation of their sense of reality", to also include non-abduction cases where absurd, hallucinatory or dreamlike events are associated with UFO encounters.
[12] Several years after Vallee's classification updates, some preferred that a close encounter of the fifth kind instead refer to human-initiated contact with extraterrestrial life forms or advanced interstellar civilizations, claiming direct communication between aliens and humans.
[16] While technically not an extension of the Vallee scale that measures result-oriented data, this replacement of the originally coined CE5 classification has become popular in marketing human-initiated contact events.
[citation needed] In a CE5 event, individuals or groups use specific protocols to establish communication or interaction with extraterrestrial beings.