The worldwide introduction of English as a medium of instruction (EMI) programmes has stimulated numerous reflections within and outside academia. These reflections find their expression in both scholarly studies into EMI and public debates about its impact. In this article we argue that one can distinguish two types of reflections about EMI. The first type focuses on improving EMI. The second type focuses on the legitimation of EMI, that is whether EMI programmes are justified in view of their assumptions and consequences. We investigate the genesis and the differences between two separate discourses that express the different types of reflections. We unfold a history that shows that roughly three phases can be distinguished in the development of EMI: the incubation of EMI, its consolidation and its politicisation. We argue that the heuristic value of the two types of reflection is that they are conducive to comprehending this development of EMI and look at it with critical eyes. In addition, we suggest that politicised issues like the impact of Englishization on the cultural identity, language hierarchies, top-down implementations of language policies and the inequalities regarding the access to EMI programmes might be fruitfully addressed in terms of linguistic justice and democracy. By distinguishing two types of reflection, blind spots in EMI research can be revealed.