This paper tries to display that a particular phrase, ‘to differ only in dialect’, was coined before the middle of the sixteenth century in the Zurich region as an effective method to describe the shallow nature of the differences between two speech varieties. Deriving from commentaries on the historiographic works of the classical Latin authors Caesar and Tacitus, this originally Neo-Latin phrase became widely employed in other text types from the 1560s onwards (chiefly in works on ethnic history, language, and theology), where it served a broad set of varying aims and discursive strategies. From the seventeenth century onwards, the collocation ‘to differ only in dialect’ affected theoretical reflections on the conceptual pair ‘language’ and ‘dialect’. This case study thus displays that scholars interested in the emergence and evolution of a concept could gain greatly from closely exploring collocations and their history.