Negligence Torts: Causation


Stubbs v. City of Rochester

Cause in Fact (“but for”)

  • When unclear, leave it to jury to make the determination (Stubbs)

  • The “but for” test: Had the defendant not acted negligently, the plaintiff's injuries would not have resulted.


  1. A negligent act was deemed wrong because the act increases the chances that a particular type of accident would occur; and

  2. A mishap of that very sort did happen, this is enough to support a finding by a trier of fact that the negligent behavior caused the harm.

  3. The plaintiff must then show that the harm was proximate. Proximate cause is when the defendant’s action occurs so near the injury that it is deemed to be the cause of the injury. In other words, there must be a close causal connection, not a long chain of events.

When such a strong causal connection exists, the burden shifts to the defendant to show that the wrongful conduct was not a substantial cause or proximate cause. Plaintiffs can use different approaches to prove causation, including expert testimony.

Multiple Possible Causes

If there are two or more possible causes of the plaintiff's injuries, it is sufficient for the plaintiff to prove with reasonable certainty that the direct cause of harm resulted from the defendant's actions

Reasonable Certainty Test

If there’s more than one potential cause, but you can’t be sure which is the cause, use the reasonable certainty test.

  1. It is sufficient for the π to prove with reasonable certainty that the direct cause of harm resulted from the defendant’s actions.

    1. The plaintiff must use evidence to establish “reasonable certainty”

  2. Plaintiff is not obligated to prove that the alternative causes (including those unknown) were the not the injury’s actual cause.

  3. But-for causation is inappropriate for multiple causes.


Summers v. Tice

Joint Tortfeasors

There can be multiple defendants who were the “but for” causes of an event. When this occurs.

  • If their combined negligence created the harm, they can each be responsible

Multiple fault

If the plaintiff can show that each of two or more defendants was at fault, but only one could have caused the injury, the burden shifts to each defendant to show that the other caused the harm. (Summers v. Tice)

Summers does not hold that every time a plaintiff sues more than one defendant the burden of proof shifts to the defendants on the issue of causation. It is a very narrow holding, and only applicable where a “but for" analysis in causation fails

Mechanics of Joint and Several Liability (J&SL)

  1. Plaintiff sues one or all of the defendants to recover full extent of damages

  2. Any solvent defendant can be liable for entire award

  3. Proportioning damages:

    1. Current rule.: Factfinder assesses fault percentages comparatively on defendants and then applies the state J&SL statute

    2. Previous rule: If a defendant paid more than his/her “share,” he/she could assert a “contribution” claim against other defendant’s. The shares were determined pro rata; not based on comparative fault

  4. It doesn’t matter if the defendants acted in concert or independently


Hymowitz v. Eli Lily

Market Share Theory

In product liability cases, courts often apply a market share theory. If the plaintiff cannot prove which of three or more persons caused his injury but can show that all produced a defective product that caused the injury, the court will require each of the defendants to pay that percentage of the plaintiff's injuries which that defendant’s sales bore to the total market sales of that type of product at the time of injury. Courts usually use a national market share, but sometimes they limit it to a state or handful of states.

  • In some states, if the company proves it didn’t cause the harm, it can get out of being held liable

Hymowitz focuses more on risk of injury and doesn't allow exculpation because the court said the defendants were part of broader risk-taking scheme, even if they didn't cause injury in a particular case.