Machine Learning from Legal Precedent

When training a machine learning (ML) model with court decisions and judicial opinion, the result of these rulings is the training data needed to optimize the algorithm that determines an outcome. As lawyers, we take the result of these rulings as final. In some cases, however, the law requires change when rulings become antiquated or conflict with a shift in regulations. This cursory report explores the level of detail needed when training an ML model with court decisions and judicial opinions.   


Much of the time, attorneys know that the law is relatively stable and predictable. This makes things easier for all concerned. At the same time, attorneys also know and anticipate that cases will be overturned. What would happen if we trained AI but failed to point out that rulings are at times overruled? That’s the mess that some using machine learning are starting to appreciate.

Make sure to read the full paper titled Overturned Legal Rulings Are Pivotal In Using Machine Learning And The Law by Dr. Lance B. Eliot at

(Source: Mapendo 2022

Fail, fail fast, and learn from the failure. That could be an accurate summary of a computational system. In law, judicial principles demand a less frequent change of pace. Under the common law principle of stare decisis, courts are held to a precedent that can either be a vertical or horizontal rule. Vertical stare decisis describes lower courts are bound by higher courts ruling whereas horizontal stare decisis describes an appellate court decision can become a guiding ruling but only for similar or related cases on the same level. In essence, stare decisis is meant to instill respect for prior rulings to ensure legal consistency and predictability. 

In contrast, the judicial process would grind to a halt if prior decisions could never be overturned or judges wouldn’t be able to deviate and interpret a case without the dogma of stare decisis. Needless to say, overturning precedent is the exception rather than the rule. According to a case study of 25,544 rulings of the U.S. Supreme Court of the United States from 1789 to 2020, the court only overturned itself in about 145 instances, or 0.56%. While this number might be considered marginal, it does have a trickle-down effect on future court rulings at lower levels. 

A high-level description of current ML training procedures could include the curation of a dataset comprised of court decisions, analysis, and legal briefs in a particular field that is used to train an algorithm to process the essence of these court decisions against a real-world scenario. On its face, one could argue to exclude overturned, outdated, or dissenting rulings. This becomes increasingly difficult for legal precedent that is no longer fully applicable yet still recognized by some of the judiciary. Exclusion, however, would lead to a patchwork of curated data that would not be robust and capable of reaching legal reasoning of high quality. Without the consideration of an erroneous or overturned decision, a judge or an ML system could not develop a signal around pattern recognition and sufficiently adjudicate cases. On the other hand, mindlessly training an ML model with everything available could lead the algorithm to amplify erroneous aspects while ranking lower current precedents in a controversial case. 

This paper offers a number of insightful takeaways for anyone building an ML legal reasoning model. Most notably there is a need for active curation of legal precedent that includes overturned, historic content. Court decisions and judicial opinions must be analyzed for their intellectual footprint that explains the rationale of the decision. Once this rationale is identified, it must be parsed against possible conflicts and dissent to create a robust and just system.      

One thought on “Machine Learning from Legal Precedent”

Leave a Reply