What is the relationship between politics and morality? In this chapter, I discuss Nagel’s dualism and Murphy’s monism in depth. Both of them limit their discussions to distributive justice, but they admit that their views can apply to a more general discussion of the relationship between politics and morality. On one hand, Nagel argues that distributive justice can only be assured by nation-states because only states have associative responsibility; associative responsibility does not apply to any particular individual. On the other hand, Murphy argues that we should assure justice by both institutions and individuals, and only monism could explain why a person should act to assure justice in nonideal situations. Both arguments have strengths and weaknesses. Nagel tells us how important sovereignty is, and Murphy tells us how important it is to assure justice. Nevertheless, Nagel fails to explain why individuals are not required to assure justice, and Murphy fails to explain how principles of justice can apply to individuals. The most important problem is that they do not have the same standard to evaluate and justify both positions. Although both of them have their own reasons to support their own view, it is unclear how they can refute the opposite side. I suggest that supervenience is the key to solve this problem. I use supervenience as a standard to evaluate arguments from both sides, and then argue that a supervenience relationship between politics and morality would be the third and better position than both dualism and monism.