This paper is concerned with argumentation in legal proceedings, namely in criminal cases. My interest is to explore how in the legal realm different argumentation fields interact, the juridical field being just one of them. The paper lays out an approach of studying argumentation in the legal realm in the framework of an ethnographic methodology by identifying the “topical rules” the participants in criminal trials adhere to. Suggesting the notion of field-dependence as a good starting point for the analysis of (...) legal argumentation, I will give several examples of different fields of argumentation interacting in criminal proceedings. The examination of what counts as a good reason and how arguments are employed, negotiated, and evaluated within a criminal proceeding might shed light on the practice of constructing facts and arriving at decisions in court. It can furthermore point at the constitution of legal rationality and how it is produced in criminal trials. I argue that rationality in criminal proceedings is interactively accomplished by negotiating different standards of validity. (shrink)