The fact that we do not know certain things gives rise to the idea of probabilities. Because we view the world as determined in assuming that every event has a cause, the probability of an event depends on a combination of what we do know and what we do not know. Laplace’s theory of probability was that if there is no reason to believe that one of a number of events, n, will occur, then the probability of each happening is 1/n. For example, the probability that any day of the week chosen at random will be either a Tuesday or a Thursday is 2/7.