Niebuhr's Moral Man and Immoral Society is a look on politics and ethics. Niebuhr focuses on the importance of justice. Niebuhr is trying to discover what justice is, and whether or not it is possible to determine if nations are progressing or regressing towards justice. Niebuhr raises the question of whether or not it is possible to achieve perfect justice. He also questions why anyone should strive for perfect justice if it is unachievable. He uses Moral Man and Immoral Society to explain why a political utopia is impossible to achieve. He argues that although perfect justice cannot be achieved, it is possible to come close to a political utopia. He discusses achieving justice through reason and through ethics. He makes the claim that there is a fundamental difference between individual morality and group morality. He argues that it is impossible to expect everyone, whether internationally or within a state, to act morally toward one another. Humans are not capable of this because vices inherent to individuals are extended to larger groups in society. States are not people and do not have sole consciousness. Humans have different identities, such as religious affiliation and wealth, so it is not possible to please everyone within a society. In order to achieve the best approximation to ultimate justices, there must be a group within a society that believes this ultimate justice is possible, or knows it is not, but thinks it is worth it to strive anyway.
A political utopia, internationally or within a state, is not possible. Although perfect justice is not possible, it is possible to come close to it – this argument separates Niebuhr from liberals and realists. Niebuhr discusses two groups called Rationalists and Moralists. Rationalists believe perfect justice is achievable through reason. An example of this would be a group of five friends going to dinner and each friend takes a turn picking where to eat.