On the campaign trail, then-candidate Donald Trump expressed a desire to pioneer an unpredictable US foreign policy that would both deceive opponents and disrupt the status quo. Academic and media commentators readily labelled this Trump's 'Unpredictability Doctrine' and have since debated its merits and demerits. Beyond inevitable partisan divides, however, these responses also revealed enormous disagreement over conceptualizations of unpredictability and its impacts, raising fundamental questions for the IR discipline and the foreign policy analysis it informs. What are the ontological and epistemological roots of unpredictability in international politics? How can scholars simultaneously grapple with the conundrums posed by erratic actors and the larger, ever-changing systems they shape? This article unravels the philosophy of science (PoS) issues inherent in theorizing unpredictability, offering a novel, synthesized typology. Recognizing that PoS assumptions both frame accounts of unpredictability and represent a source of uncertainty, this article instead advocates epistemological humility, offering a new typology that transcends assumptions and facilitates dialogue between camps. This typology includes three 'buckets' of unpredictability – risk, uncertainty and complexity – that can be interpreted according to varying philosophy of science traditions. When applied empirically, this terminology helps contextualize analysis and expose oftentimes overlooked contours of US foreign policymaking. [ABSTRACT FROM AUTHOR]