We present a diachronic analysis of multi-word expressions (MWEs) in English based on the Royal Society Corpus, a dataset containing 300+ years of the scientific publications of the Royal Society of London. Specifically, we investigate the functions of MWEs, such as stance markers (“is is interesting”) or discourse organizers (“in this section”), and their development over time. Our approach is multi-disciplinary: to detect MWEs we use Universal Dependencies, to classify them functionally we use an approach from register linguistics, and to assess their role in diachronic development we use an information-theoretic measure, relative entropy.