Utilitarianism is a theory in normative ethics holding that the best moral action is the one that maximizes utility. Utility is defined in various ways, but is usually related to the well-being of sentient entities. Classically, Jeremy Bentham, the founder of Utilitarianism, defined utility as the aggregate pleasure after deducting suffering of all involved in any action. John Stuart Mill expanded this concept of utility to include not only the quantity, but quality of pleasure, while focusing on rules, rather than individual moral actions. Others have rejected that pleasure has positive value and have advocated negative utilitarianism, which defines utility only in terms of suffering. In contrast to this hedonistic view, some define utility with relation to preference satisfaction whereas others believe that a range of values can be included in its definition.Utilitarianism is a form of consequentialism, which states that the consequences of any action are the only standard of right and wrong. This view can be contrasted or combined with virtue ethics which holds virtue as a moral good. Some believe that one's intentions are also ethically important. Utilitarianism is distinctly different from other forms of consequentialism such as egoism as it considers all interests equally. Proponents of utilitarianism have been split about whether individual acts should conform to utility (act utilitarianism) or whether agents should conform to ethical rules (rule utilitarianism). Utilitarians additionally remain split about whether utility should be calculated as an aggregate (total utilitarianism) or an average (average utilitarianism).Historically, hedonism can be traced back to Aristippus and Epicurus who viewed happiness as the only good. Bentham is, however, credited with founding utilitarianism when he wrote An Introduction to the Principles of Morals and Legislation. Since Bentham, prominent utilitarians have included John Stuart Mill, Henry Sidgwick, R.M. Hare and Peter Singer. The philosophy has been applied to modern issues including the suffering of non-human animals. Specifically, utilitarianism has been applied to the ethics of raising animals for food and the ethics of wild animal suffering. Effective altruism is a philosophy aimed at improving the world through evidence based means, which has been supported on utilitarian grounds.Opponents of utilitarianism have criticized it for many reasons. Some have said that utilitarianism ignores justice while others contend that utilitarianism is impractical. Specific criticisms have included the mere addition paradox and the utility monster. Others have said that pleasure is not commensurable across people with varying identities and thus the idea of aggregating utility is impossible.