Learned Hand
Learned Hand (1872 - 1961) was a judge at the U.S. District Court for the Southern District of New York and the Court of Appeals for the Second Circuit. One of his most famous holdings comes from U.S. v. Carroll Towing, 159 F.2d 169 (2d Cir. 1947), concerning civil liability:"[T]he owner's duty, as in other similar situations, to provide against resulting injuries is a function of three variables: (1) The probability that she will break away; (2) the gravity of the resulting injury, if she does; (3) the burden of adequate precautions. Possibly it serves to bring this notion into relief to state it in algebraic . . . terms: if the probability be called P; the injury, L; and the burden, B; liability depends upon whether B is less than L multiplied by P: i.e., whether B less than PL."
This rule is noticeable for its economic approach to a legal rule, an approach that also is the foundation of the study of "law and economics".