Visual sightings of an unidentified flying object, seemingly less than 500 feet away, that show an appreciable angular extension and considerable detail.
A UFO event in which a physical effect is alleged. This can be interference in the functioning of a vehicle or electronic device; animals reacting; a physiological effect such as paralysis or heat and discomfort in the witness; or some physical trace like impressions in the ground, scorched or otherwise affected vegetation, or a chemical trace.
UFO encounters in which an animated creature is present. These include humanoids, robots, and humans who seem to be occupants or pilots of a UFO.
A UFO event in which a human is abducted by a UFO or its occupants.This type was not included in Hynek’s original close encounters scale.
Hynek’s erstwhile associate Jacques Vallee 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”, so as to also include non-abduction cases where absurd, hallucinatory or dreamlike events are associated with UFO encounters.
The film The Fourth Kind makes reference to this category.
A UFO event that involves direct communication between aliens and humans.This type of close encounter was named by Steven M. Greer‘s CSETI group and is described as bilateral contact experiences through conscious, voluntary, and proactive human-initiated cooperative communication with extraterrestrial intelligence.
Death of a human or animal associated with a UFO sighting, although some might consider this as a more severe example of a second-kind encounter.
The creation of a human/alien hybrid, either by sexual reproduction or by artificial scientific methods.