Precognition is the ability to perceive information about future places or events before they happen. It is done by mentally scanning the various alternate futures, rather than using deduction based on current knowledge. Predicting which one of these futures one is likely to experience can never be done with perfect accuracy, since reality must diverge in order for there to be alternate futures, and hence, there will be divergent counterpart of the predictor in each of these alternate futures. Sometimes precognition is only expressed in vague dreams while asleep, other times it is clear and occurs at will and when awake. A being who possesses precognition is sometimes called a precog.