Recently, the debate between legal positivism and non-positivism has been framed as a controversy about the grounds of law. This article points out that the controversy results from their disagreement about the nature of legal obligation. According to legal positivism, legal obligations as obligations from the legal point of view are apparently rather than genuinely normative. By contrast, non-positivism holds that legal obligations are genuine obligations, i.e., moral obligations generated by our legal practices. This article defends a non-positivist view of legal obligation and attempts to explain the normative impact of social facts or institutional actions which constitute legal practices: Legal practices affect our normative reasons by changing the relevant facts and circumstances, thereby shaping the content of moral obligations.