"Instead of looking at the consequences of a particular act, rule-utilitarianism determines the rightness of an act by a different method. First, the best rule of conduct is found. This is done by finding the value of the consequences of following a particular rule. The rule the following of which has the best overall consequences is the best rule. Among early proponents were John Austin (The Province of Jurisprudence 1832) and John Stuart Mill (Utilitarianism 1861).
One problem with rule-utilitarianism is this: it invites us to consider the consequences of the general following of a particular rule. Suppose the consequences of the general following of rule R are optimal. We can say that rule R is the best rule, and that everyone ought to follow that rule. But how ought one to act if people are not generally likely to follow that rule? To illustrate: suppose that for every country, the best traffic rule is to keep to the right. According to rule-utilitarianism, I ought to keep to the right. Suppose I am in Britain and know that people will generally keep to the left...Ought I really to keep to the right?
Another problem is that the best rules would not be simple. The best rule for promise-keeping would be of the form: 'Always keep your promises except...'(where the list of exceptions would be very long). This led the American philosopher David Lyons to argue, in Forms and Limits of Utilitarianism 1965, that a plausible formulation of rule-utilitarianism would make it recommend the same actions as act-utilitarianism, so the two kinds are 'extensionally equivalent' and there is no practical difference between the two. Currently, rule-utilitarian formulations seem to be ought of favour, but there are attempts to rehabilitate them."
The Penguin Dictionary of Philosophy
ed. Thomas Mautner
The Abolitionist Project
Critique of Brave New World