Open Texture of Rules

Every rule, H. L. A. Hart argued, has an edge where its language gives out and certainty dissolves into genuine uncertainty—and what happens at that edge is the central problem of handing rules to machines. Hart borrowed the phrase “open texture” from the philosopher Friedrich Waismann and placed it at the center of his account of law. His claim was not that careless drafting produces vague rules—it was that all rules expressed in general language are necessarily open-textured, possessing a core of settled meaning and a surrounding penumbra of cases where it is genuinely uncertain whether the rule applies. His illustration has become the most famous example in modern jurisprudence: a rule that says “no vehicles in the park.” A car is clearly a vehicle; the rule plainly forbids it. But what about a bicycle? A skateboard? An ambulance responding to an emergency? A war memorial consisting of a real military truck mounted