A moral code designed for hypothetically perfectly moral beings does not address the actual desires, emotions, and irrational proclivities of real humans

For Sidgwick, Spencer’s utilitarianism was merely seemingly deductive even though it purported to be more scientific and rigorously rational than “empirical” utilitarianism. However, deductive hedonism fails because, contrary to what deductive hedonists like Spencer think, no general science of the causes of pleasure and pain exists, insuring that we will never succeed in formulating universal, indefeasible moral rules for promoting happiness. Moreover, Spencer only makes matters worse for himse