Classical utilitarians, including Jeremy Bentham, John Stuart Mill, and Henry Sidgwick, define happiness as pleasure and the absence of pain.
According to act utilitarianism, then, the right thing to do tomorrow is to go out and do charity work; it is wrong to stay home and watch television all day.
Jeremy Bentham supported his theory with another famous quote of his, that "Nature has placed mankind under two sovereign masters, pain and pleasure.
This means that he believed people would actively seek out pleasure and avoid pain, if given the opportunity.
Critics sometimes cite such prohibitions on leisure activities as a problem for act utilitarianism.