So far we have considered something being ‘true’ or ‘ not true ‘ or ‘not known’ . there is also the situation ‘probably true’. In situations where “the relevant world is random” or “appears to be random because of poor representation “ or “not random but our program can not access large data base”, probabilistic reasoning is to be applied. (Example of such situations are – motion of electron, a drug being successful on a patient etc,). One has to apply probabilistic reasoning in deciding about the next card to play in a game of cards or in diagnosing the illness from the symptoms. These are random world. Uncertainties can arise from an inability to predict outcomes due to unreliable, vague, incomplete or inconsistent knowledge.