Description:
<jats:title>Abstract</jats:title><jats:p>Within the framework of scientific argumentation, this study explores the role of what we here call the<jats:italic>unstated argument</jats:italic>in knowledge construction. The case study conducted in a cancer research lab in Brussels, uses observation, open interviews, and discourse analysis. Guided by Discursive Psychology as a theory and method, it examines the bases of a specific<jats:italic>unstated argument</jats:italic>embedded in<jats:italic>tacit knowledge</jats:italic>. The unstated argument is about<jats:italic>medium usage</jats:italic>in cancer research. The medium is a chemical liquid composed of a number of substances injected into the cells that scientists use to carry out experiments. The findings suggest that the unstated argument comprises a claim and de facto evidence. The claim is that the medium usage is appropriate and not problematic for research results. The evidence: (1) does not emanate from research; (2) is based on<jats:italic>personal opinion</jats:italic>; and (3) is backed up by the following factors: (a) practicing the status quo; (b) adhering to cancer-research standards; and (c) being bound by the demand and supply interplay. Provoked by the present study, counterevidence is ultimately substantiated by the same scientists. The counterevidence happens to challenge the claim, as it is based on<jats:italic>expert-opinion</jats:italic>. The study suggests that ethnography can offer a unique methodological stance to discern the unstated arguments embedded in tacit knowledge.</jats:p>