Utilitarianism is a theory, which first became widely acknowledge when it was adopted by its greatest advocate Jeremy Bentham. It is a theory that maintains that it is an action's total consequence that determines its moral correctness. It is a theory not concerned with the effects of the action on the individual carrying out the action, but instead the effect it has on everybody affected by the action. It also maintains that it is happiness that is key to life's conquest, and hence happiness that is the determination of right or wrong. Very simply if an actions consequence cause happiness, then the action is right, if it causes pain, or destroys happiness then the action is wrong. The main philosophy of the theory of Utilitarianism is to create the greatest happiness for the greatest number.
Jeremy Bentham, and his disciple John Stuart Mill have become recognised as the two greatest sponsors of Utilitarianism. Bentham is known for his popularisation of the more traditional version of the theory, know as Act Utilitarianism. Although a student of Bentham, Mill could see problems in what he was being taught and so began to develop his own views on Utilitarianism, which are now known as Rule Utilitarianism.
Bentham was a great traditionalist believer in the expression, "the greatest good for the greatest number." Bentham called this principle the principle of utility. With "utility" here referring to the tendency of an action to produce happiness, not its usefulness. It is the aim of Act Utilitarianism to fulfil to the greatest extent the principle of utility.
Act Utilitarianism focuses solely on the consequences of the action. The motives and the reasons why actions are carried out are trivial in determining the moral rightness of the action; yet is the value of the consequences of the particular act that counts when determining whether the act is right. So if I killed somebody, and my intent was