Utilitarianism is a teleological theory. This means that an act is judged to be moral, based on its consequences, rather than its motives. It is based on the principle "the greatest good for the greatest number". Therefore, an act is moral if it results in the greater happiness of the majority.
There are three main types of utilitarianism:
Act Utilitarianism: this deals with the consequences of individual acts, and follows no absolute rules, except that the greatest good is produced for the greatest number.
Rule Utilitarianism: This allows certain absolute rules to be followed, (for example 'do not kill') i.e. those that society has established to allow the greatest good to the greatest number.
Preference Utilitarianism: says that you should act in a way that the person involved prefer, unless that preference is outweighed by others.
The pioneer of the utilitarianism theory was Jeremy Bentham. He lived from 1748-1832 and was brought up in a very intellectual family. Both his father and grandfather were lawyers and so he was expected to follow them into law.
While reading Priestly's Essay on Government he found the principle "the greatest good of the greatest number". He decided to apply this principle to all the areas of social activity. His main passion was legislation. He had said that "It is the legislator who alone has the power of determining the conditions under which men live", and so he applied the principle to this aspect of social life first. He was responsible for many criminal law reforms, the abolition of transportation and imprisonment for debt. He helped to develop cheap postage and the registration of births and deaths.
He later applied it to morals by arguing "...The principle of utility is meant the principle which approves or disapproves of every action whatsoever, according to the tendency which it appears ti have to augment or diminish the happiness of the party whose interest is in question.