Understanding the reasoning of others is a key aspect to achieving a shared understanding when collaboratively solving a problem, such as the generation of a plan, and recent observations of military planners suggest that it plays a key role in the planning process. An example of rationale is described where a misunderstanding is only resolved by the joint exploration and cross-challenging of the rationale. A prototype tool is described that permits the creation and visualization of the basic rationale via the use of a Controlled Natural Language derived from Common Logic Controlled English. Using the example, the paper explores mechanisms that could potentially make more effective use of rationale.