<p>The External Incentives Model (EIM) is widely cited as a rationalist explanation of Europeanisation among non-member states, yet its analytical foundations remain unclear. Is it a model of strategic bargaining, a framework of conditional compliance, or a non-strategic cost–benefit formulation? This article reconstructs the EIM within a three-dimensional typology of bargaining models, identifying internal inconsistencies and underspecified assumptions about actors, sequencing, information, and equilibrium concepts. We then show that the EIM’s core hypotheses can be derived from multiple causal logics, leading to a problem of underdetermination: distinct models produce empirically indistinguishable predictions. Finally, we argue that restating the EIM on explicit formal foundations clarifies its testable content and limitations, thereby strengthening theory-building and improving the comparability of empirical research on EU enlargement and conditionality. More broadly, the analysis contributes to efforts in comparative European politics to align theoretical claims, modelling assumptions, and empirical strategies more rigorously.</p>