Happiness as the constitutive principle of action in Thomas Aquinas

Constitutivism locates the ground of practical normativity in features constitutive of rational agency and rests on the concept of a constitutive norm - a norm that is internal to a thing such that it both defines and measures it. In this essay, I argue that Aquinas understands happiness as the constitutive principle of human action, since happiness is the end that both defines and measures it. Turning to the thought of Aquinas opens up new possibilities for constitutivism by showing how the constitutive principle of action can be the ground of a practical realism in ethics.