Proximate Cause

1. A cause that is legally sufficient to result in liability; an act or omission that is considered in law to result in a consequence, so that liability can be imposed on the actor.  2. A cause that directly produces an event and without which the event would not have occurred.  — Also termed (in both senses) direct cause; direct and proximate cause; efficient proximate cause; efficient cause; efficient adequate cause; initial cause; first cause; legal cause; procuring cause; producing cause; primary cause; jural cause. Cf. (in sense 2) remote cause.
“The four ‘tests' or ‘clues' of proximate cause in a criminal case are (1) expediency, (2) isolation, (3) foreseeability and (4) intention.” Rollin M. Perkins & Ronald N. Boyce, Criminal Law 823 (3d ed. 1982).
“ ‘Proximate cause’ — in itself an unfortunate term — is merely the limitation which the courts have placed upon the actor's responsibility for the consequences of the actor's conduct. In a philosophical sense, the consequences of an act go forward to eternity, and the causes of an event go back to the dawn of human events, and beyond. But any attempt to impose responsibility upon such a basis would result in infinite liability for all wrongful acts, and would ‘set society on edge and fill the courts with endless litigation.’ [North v. Johnson, 58 Minn. 242, 59 N.W. 1012 (1894).] As a practical matter, legal responsibility must be limited to those causes which are so closely connected with the result and of such significance that the law is justified in imposing liability. Some boundary must be set to liability for the consequences of any act, upon the basis of some social idea of justice or policy.” W. Page Keeton et al., Prosser and Keeton on Torts § 41, at 264 (5th ed. 1984).

Black's Law Dictionary (9th ed. 2009)