This essay argues that the work of ministries of foreign affairs (MFAs) centres on three modes of articulation; namely, intersubjective, practical and material articulations. However, much research in diplomatic studies has yet to come to terms with the specific ways in which these modes of articulation coalesce to produce a distinctive foreign policy. I suggest that a field theory account of MFAs offers a reliable set of tools that enables us to understand how a foreign policy takes shape, the dynamics that sustain it and the circumstances under which it is likely to change. Because a field’s existence is often derived from its relational consequences, the essay clarifies the link between a field and its effects, using the concept of ‘affordance’. In this sense, theorising MFAs connects a philosophy of action — which focuses on the field theory’s concepts — and a philosophy of science — which emphasises relations within and between different modes of articulation.