Clairvoyance is paranormal knowledge of some objective event not necessarily involving another mind. Precognition is paranormal knowledge of future events - knowing the future before it happens, provided that we could not have figured out or inferred what was to happen, and provided chance or coincidence was not involved. Telepathy, clairvoyance, and precognition are usually known to the layman as extrasensory perception or ESP phenomena. Parapsychology is another name for the discipline which studies these sorts of phenomena.
Parapsychologists have two basic approaches to their subject matter.
These cases are usually quite dramatic, very compelling and convincing to the persons experiencing them, and are useful in suggesting leads about the conditions under which psychic phenomena occur. Scientifically, though, they are not very convincing. The other approach is to attempt to study psychic phenomena in the laboratory. Here, under well-controlled conditions, uncertainties may be eliminated and valid conclusions may be reached about the existence and nature of these phenomena. Science is concerned with understanding the phenomena and laws of the universe.