Ever self-conscious about its purpose and method, the discipline of International Relations (IR) has long debated questions about its most basic relevance, such as what to study and for what purpose. This has led to several complaints about incommensurability between different approaches to the subject, and therefore a lack of progress and knowledge production. Recently, several scholars have advocated a more inclusive debate between different theories and philosophies in IR. This article attempts to evaluate the extent to which scholars, using different theoretical perspectives, can produce meaningful knowledge in IR. It will focus on the two most prominent theoretical approaches to IR; realism and liberalism, which have more in common than the more divided philosophies of science, that make up the field. Drawing on the recent debate about ”No Kill Zones” in Syria, proposed by Anne-Marie Slaughter, and criticized by Stephen Walt, the article will illustrate the limits and possibility of producing knowledge about international relations through debates between theories, which rely on incommensurable foundations. To evaluate this, it will draw on three prominent philosophers of science: Karl Popper, Max Weber, and Thomas Kuhn. This will lead to the argument that there is no possible resolution for inter-theoretical debates, like the one between Slaughter and Walt, from the application of scientific method or set guidelines, and that incommensurability remains a feature of IR. We should therefore seek to engage in inter-theoretical debates, where possible, instead of trying to settle these theoretical debates themselves. To do so, this article suggests that the traditional “bottom-up” approach to evaluating incommensurability should be replaced with a “top-down” approach, which enables such limited inter-theoretical debate, through an open conversation beginning with conclusions rather than foundations. Firstly, however, it will discuss theoretical divisions in IR, and incommensurability in general.
