For a little more than twenty years, the terminology used in the economics of science has changed significantly with the development of expressions such as ‘new economics of science’ (NES) and ‘economics of scientific knowledge’ (ESK). This article seeks to shed light on the use of these different terminologies by studying the work of the economist of science Paul David. We aim to use his work as a case study in order to argue for a difference between NES and ESK and to show, in a concrete way, the sociological ambiguities now going on in the economics of science.