 Timothy Williamson (1994) traces our ignorance of the threshold for childhood to “margin for error” principles. If one knows that an \(n\) day old human being is a child, then that human being must also be a child when \(n + 1\) days old. Otherwise, one is right by luck. Given that there is a threshold, we would be ignorant of its location. Under a use theory of meaning, the threshold depends on many speakers. Williamson characterizes this threshold as sharing the unpredictability of long term weather forecasts. According to the meteorologist Edward Lorenz, a tornado in Kansas could be precipitated by the flapping of a butterfly’s wings in Tokyo. 