What is Act Utilitarianism? How does this form a moral choice?

Utilitarianism is an ethical theory concerned with the consequences of actions rather than the motivations. There are two types of utilitarianism, Act and Rule, and this answer will focus on the first of these. Utilitarianism is driven by the principle of utility, which is the belief that actions are right when they promote happiness or pleasure and wrong when they produce unhappiness or pain. Act Utilitarianism was developed by Jeremy Bentham, who believed that people are driven by two sovereign masters, pleasure and pain. He believed the principles of equality and fairness should be central to ethics, and that acts which produce the most happiness are morally virtuous. To help calculate which acts create the most happiness or pain, he formulated the Hedonic Calculus. This calculus measures seven aspects of pleasure and pain: duration, intensity, certainty, remoteness, fecundity, purity and extent. An act utilitarian would make a moral choice through application of the principle of utility and the hedonic calculus on a case by case basis. To an act utilitarian it is the value of the consequences of an act that counts, therefore an individual can commit a crime if it produces greatest happiness. It is flexible, allowing moral rules situational adaptation.