In the last few decades, some judges have used diagrams and other images in decisions to explain their reasoning. This thesis seeks to understand how images can function to improve and clarify legal decision-making. To understand the benefits of using images for these purposes, this thesis examines the struggle to understand the rationality of legal reasoning, the role of formal and informal logic, and the cognitive psychology of how images are employed to make decisions in fields other than law. With this background, the use of images can be expanded to aid the process of drawing conclusions in oral and written legal argument and decision-making. In the process of recommending how to use images in legal reasoning, this thesis counters historical biases within the legal profession against using logic and images.