Michael Polanyi and H.M. Collins contrast tacit knowledge with explicit knowledge. For Collins, secrets and other forms of “relational tacit knowledge” are tacit, but only in relation to specific circumstances and relationships. Collins treats such relational knowledge as less interesting theoretically than collective knowledge that is essentially difficult and perhaps impossible to convey through explicit formulations. In this paper I focus on relational tacit knowledge, despite its marginality in Collins’s typology, because it draws attention to conceptual ambiguities in the relationship between tacit and explicit knowledge. More importantly, such ambiguities come into play as strategic resources in historical labor conflicts and in efforts to secure and preserve professional autonomy. Instead of treating tacit knowledge as a substantive possession of individuals and groups, I suggest that an empirical sociological alternative is to investigate pragmatic and polemical uses of the tacit/explicit distinction in particular circumstances of action and conflict.