As long as science has been around, researchers have dealt with phenomena that cannot be explained. This is due to the fact that they do not have any way of testing whether the phenomena is real or not. One of these unexplained ideas is called Extrasensory Perception, or ESP. Extrasensory Perception is the belief that one can perceive certain events or stimuli without using there senses, like touch or seeing. Researchers have divided Extrasensory Perception into three major groups, precognition, telepathy, and clairvoyance. The first group is precognition; this is the idea that people can predict future events. They can tell what is going to happen before it actually does, they do this through means that cannot be explained with science. The next group is telepathy; this is the reading of other people's minds. The last group is clairvoyance, or the detection of hidden objects or things we cannot see. The problem with ESP is that researchers have a tough time validating claims. They have no real way of testing whether ESP is real or not. They have to rely on things like asking participants to identify the card they are about to flip. Some tests have proven that people have actually done it, but there is no way of telling if it was luck or ESP. Also, many of the tests cannot be replicated. This is one of the key characteristics of scientific thinking, replicability. The fact that there is no valid way of testing whether or not ESP is real means that we cannot completely believe in it. It is like ghosts, we can choose to believe in them, but we still do not know if they are real or not.