The precedent that was narrow

A court decided a case about a photograph taken in a park, and within a year the judgment was being cited in arguments about facial recognition, workplace cameras and school attendance systems. The judges had been careful to say that it decided none of those things.

A judgment contains two kinds of statement. The ratio is the reasoning necessary to reach the decision on the facts before the court, and it binds later courts. Everything else is obiter: observations, examples, cautions about matters not argued. The distinction is old and contested at the margins, and it exists because a court is deciding a dispute between two parties rather than legislating. A judge who ruled on every related question would be writing a statute without the evidence or the mandate that a legislature has.

What happens in practice is that the obiter travels. It is quotable, it reads like a general principle, and it is often the most interesting prose in the document. Advocates cite it because it helps; journalists cite it because it is comprehensible; and after enough citation a line that was explicitly not decided acquires the appearance of settled law.

The corrective is unglamorous. Read the facts first, then ask what the court could not have avoided deciding. A sentence that would still have been written had the facts been different is an observation, and an observation from a senior judge is worth attention and is not a rule.

The park case illustrates the point from the other side. Its ratio turned on a detail that nobody quotes: whether the photographer had been asked to stop. Every application of the case to a camera that cannot be asked anything is therefore an extension rather than a citation, and the courts have since said so twice.