PROXIMATE OR LEGAL CAUSE
The plaintiff must prove the defendant's culpable conduct is the proximate cause of the plaintiff's injuries. “Proximate” or “legal” cause adds to the requirement that the defendant's culpable conduct be the actual cause of the plaintiff's injury and will preclude recovery when the causal relationship between the defendant's conduct and the plaintiff's injury does not justify imposing tort responsibility on the defendant.
[A] Foreseeability Test - Definition
The leading test for proximate cause focuses on whether the defendant should have reasonably foreseen, as a risk of her conduct, the general consequences or type of harm suffered by the plaintiff. In essence, the foreseeable harm test requires (1) a reasonably foreseeable result or type of harm, and (2) no superseding intervening force. The extent and the precise manner in which the harm occurs need not be foreseeable. [See, e.g., “Wagon Mound No. 1” (Overseas Tankship (U.K.), Ltd. v. Morts Dock & Engineering Co., Ltd.,  A.C. 388).]
An intervening force is a new force which joins with the defendant's conduct to cause the plaintiff's injury. It is considered intervening because it has occurred sequentially in time after the defendant's conduct. If the intervening force is characterized as superseding, proximate cause is not established even though the type of harm is foreseeable. An intervening force is generally characterized as superseding only when its occurrence appears extraordinary under the circumstances. [See, e.g., Derdiarian v. Felix Contracting Corp., 414 N.E.2d 666 (N.Y. 1980).]
[B] “Egg-shell” Plaintiff Personal Injury Rule
While foreseeability of consequences is generally required to find liability, courts make an exception and do not require that the type of personal injury suffered by a victim be foreseeable. [See, e.g., Keegan v. Minneapolis & St. Louis R.R. Co., 78 N.W. 965 (Minn. 1899).] The defendant is liable even if the victim suffers physical injury far more severe (e.g., heart attack) than the ordinary person would be anticipated to have suffered from the accident.
More controversial is whether psychological sensitivity should also be covered under the egg-shell plaintiff rule. Some courts have so held, such as when a minor automobile accident resulted in the plaintiff's suffering a severe psychological breakdown. [See Steinhauser v. Hertz Corp., 421 F.2d 1169 (2d Cir. 1970).]
[C] The Direct Test
The direct test would find proximate cause satisfied whenever the defendant's negligence caused the injury without any intervening force. While once very widely accepted [see Polemis, Furness, Wilty and Co., 3 K.B. 560 (1921)], it is questionable whether the direct test has any viability in contemporary law.
[D] “Practical Politics” and “Rough Sense of Justice” Test
In a famous dissent to Chief Justice Cardozo's opinion in the renowned Palsgraf v. Long Island R.R., 248 N.Y. 339 (N.Y. 1928), decision, Justice Andrews considered the appropriate tests for proximate cause. Ultimately he concluded that proximate cause is a question of public policy, fairness and justice, which cannot be reduced to any mechanical formula.
On occasion, courts have explicitly quoted Justice Andrews' assertion that proximate cause is a matter of public policy and justice and not logic to justify rulings on proximate cause that could not be explained consistently with the application of other standards, such as the foreseeability test. [See, e.g., Kinsman Transit Co. v. City of Buffalo (“Kinsman II”), 388 F.2d 821 (2d Cir. 1968).]
[E] Restatement Test
The Restatement utilizes the term “legal” rather than “proximate” cause. Restatement § 431 defines an actor's negligent conduct to be a legal cause if “(a) his conduct is a substantial factor in bringing about the harm, and (b) there is no rule of law relieving the actor from liability because of the manner in which his negligence has resulted in harm.” The Restatement utilizes the substantial factor requirement to encompass both actual cause-in-fact and causation in “the popular sense, in which there always lurks the idea of responsibility.” Section 433 lists considerations important in determining whether conduct is a substantial factor including: the number of other factors which contribute to harm; whether the defendant's conduct has created a continuous and active force; and the lapse of time.
Once the tortfeasor's conduct is established as a substantial factor for the plaintiff's injury, Restatement § 435 indicates that liability will not be restricted merely because the actor could not foresee the extent or the manner in which the harm occurred. The defendant will not be held the legal cause of the harm under § 433, however, if “looking back from the harm to the actor's negligent conduct, it appears to the court highly extraordinary that it should have brought about the harm.”
While the Restatement's principle of legal cause may be consistent with many decisions, the articulated comprehensive theory itself, unlike many provisions of the Restatement, has failed to gain general acceptance.