What Is Actual Cause?

In personal injury law, actual cause — often called cause-in-fact — is the first and most fundamental step in proving legal responsibility. It asks a simple but powerful question: Did the defendant’s actions actually cause the plaintiff’s injury? If the harm would not have occurred “but for” what the defendant did (or failed to do), then that conduct is considered the actual cause of the injury.

Actual cause matters because it forms the backbone of every negligence claim. Without it, there’s no link between careless behavior and real-world harm — meaning no basis for compensation. Understanding how actual cause works helps plaintiffs know what must be proven in court and why strong factual evidence can make or break a case.

What Is Actual Cause in Personal Injury Law?

In a negligence claim, a plaintiff must prove four elements: duty, breach, causation, and damages. Causation itself has two parts — actual cause and proximate cause. Actual cause focuses on the factual connection between conduct and injury. Proximate cause deals with whether that harm was foreseeable or too remote to assign legal responsibility.

Courts commonly use the “but-for test” to decide whether actual cause exists. The question is: But for the defendant’s act or omission, would the injury have occurred? If the answer is “no,” then the defendant’s action is a factual cause of the harm.

Consider this example: A driver texts while approaching an intersection, runs a red light, and hits another car. The crash happened because of the driver’s inattention — without that behavior, the collision would not have occurred. The driver’s texting is therefore the actual cause of the plaintiff’s injuries.

Key points:

• Actual cause establishes a direct, factual link between conduct and injury.

• The “but-for test” is the most common way to evaluate it.

• Multiple acts can each qualify as an actual cause if they substantially contribute to harm.

• Without proving actual cause, a negligence case cannot succeed — even if the defendant clearly acted carelessly.

How Is Actual Cause Proven in Court?

Proving actual cause requires evidence that demonstrates the chain of events connecting the defendant’s actions to the injury. This often involves expert testimony, witness statements, and documentary evidence like police reports or medical records.

Courts analyze causation by asking whether the defendant’s act set in motion a sequence of events that naturally led to the harm. If the injury would have occurred regardless of what the defendant did, actual cause does not exist.

For example, suppose a defective ladder collapses while a worker is using it. If the worker fell because the ladder broke, the manufacturer’s defect is the actual cause. But if the worker had a sudden medical emergency and fell before the ladder gave way, the defect may not be the factual cause of injury.

Takeaways:

• Plaintiffs carry the burden of proving the defendant’s action directly caused their injury.

• Physical evidence, accident reconstruction, and expert opinions help establish cause-in-fact.

• Competing explanations (like preexisting conditions or unrelated hazards) can weaken causation arguments.

• Clear documentation — photos, incident reports, and consistent medical records — often determines success.

(Learn more about proving causation in negligence from Nolo’s Legal Encyclopedia