Korsgaard (2009) argues that we can draw a conclusion about the metaethical status of instrumental rationality by considering an instrumental analogue of Carroll’s paradox. Specifically, she appeals to it to argue against metaethical realism about instrumental rationality (and about other normative principles as well).  Let’s suppose that there is a requirement of reason to be instrumentally coherent.  A realist would claim that there is some normative fact, according to which we ought to be instrumentally coherent.  But a skeptic might ask, “Why ought I apply that fact—that I ought to be instrumentally coherent—to my actions?” The realist might answer, “Because—and here’s another normative fact—it just is the case that you ought to apply the fact that you ought to be instrumentally coherent to your actions.” But one might resume one’s skepticism and ask why one must apply that normative fact to one’s actions.  One could keep adding normative facts ad infinitum without providing an answer to the question, in the same way that Achilles could keep adding premises without meeting the Tortoise’s challenge.  