Today's argumentation software mostly emphasizes the logical structure of reasoning, and especially the structure as it can be represented in boxes-and-arrows style diagrams. In this paper an alternative way of providing argumentation support is proposed. A content-oriented, relatively lowtech tool is presented, based on the knowledge structure of a legal topic, inspired by the structure of legal treatises. The design for this system builds on research in the areas of law, logic, argumentation theory and cognitive ergonomics. A small user evaluation has been performed to examine the usefulness of the system. We show that supporting legal reasoning based on the knowledge structure of a legal topic can be an interesting foundation for argumentation software.