What makes for a valid legal argument?

Three intertwined threads run through many recent editorials of the Leiden Journal of International Law (LJIL). They tie together many debates within and beyond the board of editors. The threads are those of the Journal's plural identity, the conversation about methods, and the spicy theme of interdisciplinarity. They are related for obvious reasons. Methodology forms one - not the only and perhaps not the foremost - factor in assessing submissions. We need to have an idea of good methodology for such an assessment to be possible. At the same time such an idea must not go against the plurality of perspectives or the Journal's aspiration to provide a forum to new and possibly unsettling voices. Research that cuts across disciplines seems especially valuable in this regard. But it comes with its own methodological challenges and tests the Journal's identity which is - albeit plural- that of a Journal of international law. It is against the background of these intertwined threads that I wish to offer a discussion of a central question that mirrors these recent debates: What makes for a valid legal argument?