act utilitarianism aggregation problem amartya sen an essay on the nature and significance of economic science animal welfare capability approach compensation principle consequentialism david hume economics enlightened self-interest epicurus eudaimonia extended sympathy felicific calculus game theory happiness hedonism henry sidgwick jeremy bentham john harsanyi john stuart mill kenneth arrow liberal paradox list of utilitarians mere addition paradox pain paradox of hedonism peter singer pleasure politics positive science preference utilitarianism public choice theory rational choice theory rule utilitarianism social choice and individual values social welfare function suffering two-level utilitarianism utilitarianism utility utility monster voting paradox voting system welfare economics william godwin