Module 6

Facts, proof and inference: burdens, standards, circumstantial evidence and probability

Students of law spend most of their time on rules and cases, but in practice most disputes are decided on the facts: what actually happened, and what can be proved. A lawyer who is expert on the law and careless about the facts will lose cases they should win. Reasoning about facts is a distinct skill with its own pitfalls, and many of the worst mistakes in the justice system, such as wrongful convictions based on bad statistics or on a persuasive story that was wrong, are mistakes of this kind and not of law. This module teaches the basics. It starts with three separate questions that are often run together: what happened, what can be proved to the standard that the law requires, and what follows legally. It then covers burdens and standards of proof, the nature of inference from circumstantial evidence, a short and practical introduction to probability reasoning (including the famous prosecutor’s fallacy), the power and danger of a coherent story, how to weigh a witness without relying on demeanour, and what a court may infer from missing evidence. All cases are invented, and the standards of proof are described in general terms because they vary between systems.

General education on legal reasoning and argument, using invented cases, by-laws and people. It states common principles and does not describe any one country’s law, rules of evidence or professional conduct rules, which differ and change. It is not legal advice, and it does not replace the instruction of a law school or a supervising lawyer.