The “But For” and “Substantial Factor” Tests

Determining what actually – and legally – happened in a negligence case

Actual and proximate causation are the underpinnings of the negligence system. What actually happened? What legally happened? These two questions are the crux of your case.

How do you determine actual causation?

causation, but for, substantial factor tests

First of all, you have to ask what actual causation is: “a factor without which the result in question could not happen.” Many thanks to the Legal Information Institute for that.

In English, this means that something occurred, and it would not have occurred but for a certain event.

This is deceptively simple to unravel. Here is an example:

Bob eats an ice cream cone and drops it on the bottom step of a staircase. Brenda runs down the staircase and slips on the lukewarm puddle of melting ice cream, injuring herself in the process. But for Bob dropping that ice cream, Brenda would not have been injured. Bob’s action was the actual cause of Brenda’s injury.

In order to answer the But For test, one must ask, “But for the existence of X, would Y have occurred?” If the answer is yes, then X is an actual cause of Y.

Some states use this to determine proximate cause as well. Let’s take a look at what that means.

Actual cause versus proximate cause

Actual cause refers to the genuine cause of an accident, as we saw above.

Proximate cause, on the other hand, is the legal cause, or what the law recognizes as the primary factor of the injury.

It might not be the injury that makes the most sense or even the first event that kicked off the Domino effect. Proximate cause refers to an action that produces foreseeable legal consequences.

Some states use the But For test while others subscribe to the Substantial Factor test. Tweet this

Some states use the But For test to determine proximate cause as well. For instance, if a drunk driver hits another car and causes that driver to suffer injuries, but for that driver operating a vehicle while under the influence, that accident would not have happened. It was reasonably foreseeable that if a driver was intoxicated and operating a vehicle, he would hit another car.

However, let’s say the drunk driver pulled a Dukes of Hazzard and drove off a ramp, causing an enormous spectacle. A rubbernecking driver wasn’t paying attention and hit another guy on a bike, causing damages. That wouldn’t be reasonably foreseeable and likely could not be blamed on the drunk driver.

The “Substantial Factor” test

Some states don’t follow the But For test and instead subscribe to the “Substantial Factor” test in order to determine proximate cause. Courts consider factors in determining whether the defendant’s actions were a substantial factor in causing the injury.

A substantial factor is anything that materially contributes to an injury – a reasonable person would have to think that it would cause harm or bring about a particular result.

An example of a substantial factor would be if the plaintiff was employed as a laborer, lifting heavy objects, and one day hurt himself. However, he also enjoyed playing high-contact sports and taking daily runs, so nobody could say for sure exactly how he’d hurt himself. His employer argued that there was no way to determine that lifting things at work had definitively injured him. However, the plaintiff argued that lifting heavy objects was a substantial factor in worsening his injuries. 

Causation can be tricky to figure out, and even seasoned lawyers need to double-check their references sometimes. If you’ve been in an accident and need help figuring out who is responsible, consider speaking with an Enjuris listed law firm.

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