The LLT Lab empirically investigates the argument or reasoning structures found in legal documents. An “argument” is a set of propositions that includes a single conclusion, as well as one or more premises that provide the reasons or support for believing that the conclusion is true, probable or plausible. Logic is the study of why some patterns of argument are correct and why some are incorrect. Traditional logic has focused on deductive or monotonic theories, in which the addition of new information cannot reduce the set of what is known. While we encounter such deductive patterns in legal documents, particularly in the area of rule-based reasoning, far more common are reasoning patterns that are non-monotonic, meaning that new information can lead us to revise what we had previously thought to be true, probable or plausible. The Lab not only studies the types of argument patterns in general that we find in legal documents, but also develops heuristic protocols for identifying argument patterns within specific types of documents, such as the reasoning specific to vaccine-injury compensation cases or the reasoning specific to medical malpractice cases.