DescriptionRonald Dworkin's anti-positivist argument from theoretical disagreement (ATD) in Law's Empire (1986) was one of the most significant volleys levied against legal positivism in the twentieth century. Dworkin argues theoretical disagreements about law pose a serious problem for legal positivists (like H.L.A. Hart) and that Dworkin's theory of law accounts for the existence of these disagreements in a way the positivist cannot. Scott Shapiro, in his book Legality (2011), argues his positivist theory of law, the Planning Theory, meets the challenge posed by ATD. In this thesis I provide two main reasons why Shapiro has not met Dworkin's challenge. First, Shapiro does not address the full force of Dworkin's challenge, which is to give a metaphysical account of law in cases of theoretical disagreements, not just a practical or epistemological account of legal reasoning in cases of theoretical disagreements. Second, Shapiro's theory by its own terms does not address all types of theoretical disagreements. Shapiro identifies theoretical disagreements with what Shapiro calls meta-interpretive disagreements. In fact, some theoretical disagreements about law are not meta-interpretive disagreements (that is, they are just plain interpretive disagreements). Therefore, the Planning Theory of law does not fully address ATD as it purports to.