The present communication deals with the methodology of the ergonomics field intervention process. It proposes an operationalized version of work analysis in terms of contradictions. The aim is to demonstrate that such a dialectic tool and method of representation may assist the ergonomist to frame the essence of a work activity in practical terms, swiftly and in a manner that preserves its multifaceted unity. The proposed method is inspired by two theoretical constructs (i) contradiction as used in Cultural Historical Activity Theory and (ii) regulation, as developed and used by the francophone tradition of ergonomics of activity. Two brief examples of its use are presented and a discussion is made on further developments and possible pitfalls.