Definition of Efficient Cause
The working cause; that cause which produces effects or results. An intervening cause, which produces results which would not have come to pass except for its interposition, and for which, therefore, the person who set in motion the original chain of causes is not responsible. Southland-Greyhound Lines v. Cotten, Tex.Civ.App., 55 S.W.2d 1066, 1069. The cause which originates and sets in motion the dominating agency that necessarily proceeds through other causes as mere instruments or vehicles in a natural line of causation to the result. That cause of an injury to which legal liability attaches. The “proximate cause.” Hillis v. Home Owners’ Loan Corporation, 348 Mo. 601, 154 S.W.2d 761, 764. The phrase is practically synonymous with “procuring cause.” Buhrmester v. Independent Plumbing & Heating Supply Co., Mo.App., 151 S.W.2d 509, 513. The Immediate agent in the production of an effect. Armijo v. World Ins. Co., 78 N.M. 204, 429 P.2d 904, 906.
The proximate cause of an injury is the efficient cause, the one that necessarily sets the other causes in operation, and, where a wrongful act puts other forces in operation which are natural and which the act would reasonably and probably put in action, the party who puts in force the first efficient cause will be responsible in damages for the injury proved, although immediately resulting from the other force so put in motion.
See also Proximate cause.
That's the definition of Efficient Cause in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.