Aquinas: Compatibilist or Libertarian?

Both compatibilist and libertarian models of human freedom suffer from certain deficiencies. The former, in which an agent's actions are determined by intrinsic causes, seems to undermine moral responsibility. The latter, in which an agent's actions are not determined, seems to flout the principle of sufficient reason. In this essay I endeavor to show that Aquinas' theory of human freedom, which is grounded in the disproportion between the formal object of the human will (goodness as such) and the finite goods that are the objects of human choices, skirts the difficulties of both compatibilism and libertarianism.