This essay originally published at Libertarianism.org. We come at last to the final of the five major theories of political obligation. I’ve looked at consent, gratitude (in two parts), fair play (again in two parts), and associations. Last up is natural duty, which holds that certain (kinds of) people or institutions may rule us not because of anything we did or anything they did specifically for each of us but because of characteristics they happen to have. In other words, the ruler or state (assuming it possesses necessary traits) may demand our obedience and we simply have a duty to comply.