CE1- Close Encounter of the First Kind. Witness observes a UFO, no interaction with witness or enviroment.

CE2- Close Encounter of the Second Kind. Interaction between the UFO and the enviroment...with physical effects on plants, animals, and humans.

CE3- Close Encounter of the Third Kind. UFO occupants are reported. No direct contact or communication.

CE4- Close Encounter of the Fourth Kind. Reported human contact with UFO occupants.