This short paper originates in the speech given by his author at the opening ceremony of the 5th Research Forum of the European Society of International Law. The speech provides remarks on the theme of the conference ('International Law as a Profession') and introduces the two subsequent keynote speeches by Andreas Paulus and Anne Orford. The paper particularly draws on the various sets of rationalities which enable international lawyers to act intelligibly, to be understood and to convince and allow them to stabilize meaning for the members of their epistemic community.