# Calculus of Negligence aka "Hand Rule"

Whilst reading an article on legal liability, I ran across a reference to the Hand Rule, formulated by Judge Billings Learned Hand (yes, that was his given name). Hand, who studied both philosophy and law, was a judge credited with a keen sense of honor and fair play as applied, in conjunction with Constitutional principles, to such as patents, torts, admiralty law, and antitrust law. The Hand Rule was born out of a trial where an improperly secured barge escaped its moorings and caused damage to other boats. Per the Hand Rule:

"[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. In mathematical terms: B < PL, where B is the cost (burden) of taking precautions, and P is the probability of loss, and L is the gravity of loss. Simply stated, negligence is ruled if the effort required to prevent an event is less than the likelihood that the event will occur, multiplied by the severity of the loss. This, of course, is all subjective, which is why he who hires the lawyer best able to define values for B, P, and L wins the case. I propose an alternate name for it: Fuzzy Law.

Posted  October 2012