In this chapter, we examine how generations of utilitarians have sought to justify or prove their theory. For each proof of utilitarianism there are three questions to be asked.

1. What is being proved? (For instance, is utilitarianism offered as the best account of right action or of institutional justice?)

2. What are the competitors? (Utilitarianism is the best x – compared to what?)

3. What are the background philosophical and cultural ideas of what counts as an adequate proof?

The proofs of utilitarianism make much more sense if we take the trouble to answer these three questions. A decisive moment in the history of utilitarianism is Sidgwick's introduction of a sceptical option. This significantly raised the stakes for any proof. As well as showing that utilitarianism is the best available moral theory, we must now also prove it is adequate – as we can no longer assume that the best moral theory is adequate. We shall see that late twentieth-century moral philosophy brings us full circle, as the focus on intuitions allows us (once again) to content ourselves with discovering the best available moral theory.

In the nineteenth century, the battleground was typically between utilitarianism and non-utilitarian morality. We are offered a proof of utilitarianism in general – a justification of the utilitarian tradition as a whole. In the twentieth century, as moral philosophy becomes more professionalized, different forms of utilitarianism are often in competition with one another.