Introductory remarks

In 1947 the distinguished American jurist, Judge Learned Hand, had to deal with a case of negligence against the owners of a tugboat that had caused a barge to sink. His judgment in the case included a terse summary of the issues that we are here to discuss. This is what he said: The owner’s duty. . . to provide against resulting injuries is a function of three variables: (1) the probability that [the tugboat] will break away; (2) the gravity of the resulting injury, if she does; (3) the burden of adequate precautions [to prevent her breaking away]. . . 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.