Factual Causation in Tort Law

Factual Causation in Tort Law

A defendant may have acted negligently.

A defendant may have breached a duty of care.

The plaintiff may even have suffered a serious injury.

But none of those facts, by themselves, necessarily establish liability.

There must also be a connection between the defendant’s wrongful conduct and the plaintiff’s injury.

That connection is the subject of causation.

In negligence law, causation is traditionally divided into two related questions:

Factual causation

and

Proximate or legal causation

Factual causation asks a relatively direct question:

Did the defendant’s conduct actually cause the plaintiff’s injury?

In other words:

Would the injury have occurred if the defendant had not acted negligently?

This is commonly expressed through the but-for test.

The basic reasoning is:

But for the defendant’s conduct, would the plaintiff have suffered the injury?

If the answer is no, factual causation may exist.

If the answer is yes—the injury would have happened anyway—factual causation may be absent.

Cornell Law School’s Legal Information Institute identifies causation as an essential component of negligence and distinguishes factual causation from proximate cause. Cornell Law School — Legal Information Institute: Causation

Factual causation is therefore the bridge between breach and injury.

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Where Factual Causation Fits in Negligence

A negligence claim can be organized as:

1. Duty

Did the defendant owe the plaintiff a duty of care?

↓

2. Standard of Care

What level of care did that duty require?

↓

3. Breach

Did the defendant fail to meet the applicable standard?

↓

4. Factual Causation

Did the breach actually cause the injury?

↓

5. Proximate or Legal Causation

Is the injury sufficiently connected to the breach for the law to impose liability?

↓

6. Damages

Did the plaintiff suffer legally recognized harm?

This sequence matters.

A defendant can breach a duty without causing the plaintiff’s injury.

That is why:

Breach is not causation.

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What Is Factual Causation?

Factual causation is the causal connection between the defendant’s conduct and the plaintiff’s injury.

The central question is:

Would the plaintiff have suffered the injury but for the defendant’s conduct?

If removing the defendant’s conduct from the chain of events means the injury would not have occurred, the defendant’s conduct may be a factual cause of the injury.

If the injury would have occurred anyway, the defendant’s conduct may not be a factual cause.

This sounds simple.

Sometimes it is.

But real accidents can involve multiple contributing factors, uncertain evidence, pre-existing conditions, independent events, and several negligent actors.

Those situations make factual causation considerably more difficult.

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The But-For Test

The traditional test for factual causation is the but-for test.

The court essentially conducts a thought experiment.

Imagine that the defendant had behaved properly.

Then ask:

Would the injury still have occurred?

If yes

The defendant’s conduct may not be a factual cause.

If no

The defendant’s conduct may be a factual cause.

For example, suppose a driver negligently runs a red light and hits a pedestrian.

If the driver had stopped at the red light, the pedestrian would not have been struck by that vehicle.

Therefore:

But for the driver’s negligent conduct, the injury would not have occurred.

Factual causation is established, assuming the evidence supports the conclusion.

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A Simple Example

Imagine that a driver is distracted by a mobile phone.

The driver fails to notice a pedestrian crossing the street.

The driver strikes the pedestrian.

The plaintiff suffers a broken leg.

Now remove the defendant’s negligent conduct from the scenario.

Suppose the driver had been paying attention.

The driver would have seen the pedestrian and stopped.

The collision would not have occurred.

Therefore:

Negligent distraction → collision → broken leg

The defendant’s conduct is a factual cause of the injury.

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Factual Causation Is About Events

Factual causation asks about the actual chain of events.

It is essentially a question of:

What happened?

The court reconstructs the sequence.

For example:

Defendant’s conduct

↓

Dangerous condition

↓

Accident

↓

Physical injury

↓

Economic and other losses

The plaintiff must connect the injury to the defendant’s wrongful conduct through a sufficiently supported factual chain.

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Breach Alone Is Not Enough

Suppose a driver violates a traffic rule.

That may establish evidence of unreasonable conduct.

But imagine that the driver violates the rule at an empty intersection and, completely independently, the plaintiff is injured by a falling tree several miles away.

The defendant may have acted wrongfully in some sense.

But the defendant’s conduct did not cause the plaintiff’s injury.

There is therefore no factual causation between the traffic violation and the plaintiff’s injury.

This demonstrates an essential principle:

A defendant can be negligent without being liable for every injury that happens afterward.

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Injury Alone Is Not Enough

The opposite is also true.

Suppose the defendant causes an injury but did not breach a duty of care.

For example, a driver is driving carefully and legally when another driver suddenly loses control and crashes into them.

The first driver may have factually contributed to the location of the accident in a very broad sense, but if the first driver’s conduct was not negligent, there may be no basis for negligence liability.

Thus, negligence generally requires both:

Breach

and

Causation

along with the other required elements.

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The But-For Thought Experiment

A useful way to apply factual causation is to imagine removing the defendant’s conduct.

Ask:

What would have happened if the defendant had exercised reasonable care?

If the injury disappears from the hypothetical sequence, factual causation is supported.

If the injury remains exactly as it would have occurred, factual causation is weakened or absent.

This is sometimes called the counterfactual analysis.

It compares:

What actually happened

with

What would have happened without the defendant’s wrongful conduct

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Counterfactual Reasoning

Suppose a doctor negligently fails to diagnose a serious disease.

The patient later dies.

The plaintiff must establish more than:

“The doctor made a negligent mistake.”

The plaintiff must establish a causal connection.

The relevant counterfactual question may be:

If the doctor had acted according to the applicable standard of care, would the patient’s outcome probably have been different?

If the patient would have died at the same time regardless of the doctor’s conduct, factual causation may be absent.

If timely diagnosis and treatment would probably have prevented or substantially changed the outcome, factual causation may be established, subject to the applicable jurisdiction’s evidentiary standards.

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Factual Causation and Medical Malpractice

Medical cases illustrate why factual causation can be difficult.

A patient may already have a serious disease.

The physician may then make a negligent error.

The patient subsequently suffers harm.

The defendant may argue:

“The disease, not my conduct, caused the injury.”

The plaintiff may respond:

“Your negligence made the outcome worse.”

The court must determine what would probably have happened without the negligent conduct.

This can require expert medical evidence.

The question is not merely whether the physician acted improperly.

It is whether that improper conduct actually changed the patient’s outcome.

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Preexisting Conditions

A plaintiff’s preexisting medical or physical condition can complicate factual causation.

Suppose a defendant negligently causes a collision involving a plaintiff who already has a weakened back.

The plaintiff experiences severe pain after the accident.

The defendant may argue that the plaintiff’s preexisting condition caused the pain.

But that does not necessarily defeat causation.

The relevant question may be whether the defendant’s conduct:

• caused the new injury;
• aggravated the existing condition;
• accelerated the plaintiff’s symptoms;
• or otherwise produced legally compensable harm.

Preexisting conditions therefore require careful causal analysis.

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The Eggshell Plaintiff Rule

Factual causation should also be distinguished from the eggshell plaintiff rule, sometimes called the thin-skull rule.

The basic principle is that a defendant generally takes a plaintiff as the defendant finds the plaintiff.

Suppose a defendant negligently pushes someone lightly.

The defendant could not reasonably know that the person had an unusually fragile skull.

The person suffers an unusually serious injury.

The defendant may still be responsible for the legally attributable consequences of the wrongful conduct.

The plaintiff’s unusual vulnerability does not necessarily break factual causation.

The rule primarily concerns the extent of liability for consequences once causation and the other elements have been established.

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Multiple Causes

Many injuries have more than one cause.

Suppose a plaintiff is injured because:

• one driver speeds;
• another driver fails to brake;
• the road is poorly maintained;
• and the plaintiff is distracted.

Which factor caused the injury?

Possibly several.

The law does not always require one single cause.

An injury can have multiple factual causes.

The challenge is determining whether the defendant’s conduct was sufficiently connected to the injury under the applicable causation doctrine.

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Concurrent Causes

Two or more acts can sometimes operate together to produce an injury.

For example:

Driver A negligently speeds.

Driver B negligently turns into an intersection.

Their vehicles collide and injure a passenger.

The injury may result from the combined conduct of both drivers.

Each defendant’s conduct may potentially be a factual cause.

The existence of another cause does not automatically eliminate causation.

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Independent Causes

Other cases involve independent events.

Suppose a defendant negligently leaves a dangerous object on a sidewalk.

Before the plaintiff reaches it, an unrelated third party suddenly pushes the plaintiff.

The plaintiff falls and is injured.

The question becomes whether the defendant’s conduct actually caused the injury.

If the plaintiff would have been injured in precisely the same way because of the independent event, the defendant’s conduct may not be a factual cause.

This illustrates the importance of reconstructing the actual sequence.

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Successive Causes

Sometimes different causes occur one after another.

For example:

Defendant A negligently causes an accident

↓

Plaintiff suffers an initial injury

↓

Plaintiff requires medical treatment

↓

A later event worsens the injury

Now the legal system must determine which consequences are attributable to which causes.

This can become especially complicated when the later event is:

• another person’s negligence;
• medical treatment;
• the plaintiff’s own conduct;
• or an independent natural event.

Factual causation may therefore involve a chain rather than a single event.

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Multiple Negligent Defendants

Suppose two defendants independently act negligently.

Both contribute to the plaintiff’s injury.

For example:

Driver A negligently strikes the plaintiff.

Driver B then negligently strikes the same plaintiff.

The plaintiff suffers serious injuries.

Determining causation may require separating:

• the injuries caused by the first event;
• the injuries caused by the second event;
• and injuries caused by both.

Different jurisdictions use different doctrines for allocating responsibility in such situations.

The key point is:

Multiple defendants can potentially be factual causes of the same injury.

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When Two Causes Are Each Sufficient

A particularly difficult causation problem arises when two independent acts are each sufficient to cause the same harm.

Imagine that two negligent actors independently create separate fires.

Either fire alone would have destroyed the plaintiff’s property.

Both fires reach the property at approximately the same time.

If the ordinary but-for test is applied mechanically, removing either defendant’s conduct might still leave the injury occurring because the other fire would have caused it.

Yet it would be artificial to conclude that neither defendant caused the destruction.

For such situations, courts may use alternative approaches to factual causation.

One historically important doctrine is associated with substantial-factor reasoning, although modern courts and jurisdictions differ substantially in terminology and application.

The precise rule should therefore always be checked under the governing jurisdiction.

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The Limits of the But-For Test

The but-for test is powerful but not always sufficient.

It works particularly well when there is one identifiable cause.

But complex cases may involve:

• multiple sufficient causes;
• multiple negligent actors;
• uncertain medical outcomes;
• preexisting conditions;
• sequential events;
• and scientific uncertainty.

In those cases, courts may use additional causation doctrines.

The important lesson is:

But-for causation is foundational, but factual causation is not always mechanically simple.

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Factual Causation and Scientific Uncertainty

Some cases involve scientific questions for which certainty is impossible.

For example, a plaintiff may allege that exposure to a particular substance caused an illness.

The plaintiff may have several possible causes of the illness.

Scientific evidence may establish probabilities rather than certainty.

Courts therefore often have to work with evidence expressed in terms of:

• probability;
• statistical significance;
• medical judgment;
• scientific studies;
• epidemiological evidence;
• and expert testimony.

The applicable burden of proof remains important.

In a civil negligence case, the plaintiff generally must prove the elements under the applicable civil standard of proof.

The precise evidentiary requirements vary by jurisdiction and claim.

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“More Likely Than Not”

In many civil cases, factual causation is evaluated under a preponderance of the evidence standard.

This generally means that the plaintiff must establish that the claimed causal connection is more likely than not.

In simplified terms:

Probability greater than 50%

may satisfy the ordinary civil burden of proof, depending on the jurisdiction and specific doctrine.

This should not be interpreted as requiring mathematical certainty.

Civil litigation frequently operates with uncertainty.

The question is whether the evidence satisfies the applicable legal burden.

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The Lost Chance Problem

Medical malpractice sometimes presents a particularly difficult causation question known as the loss-of-chance doctrine.

Suppose a patient has a serious disease.

Even with proper treatment, the patient’s chance of survival may have been limited.

A physician negligently delays diagnosis.

The patient’s probability of survival falls further.

The question becomes:

Did the negligence cause a legally recognizable injury if the patient could not prove that proper treatment would more likely than not have produced survival?

Jurisdictions differ significantly in how they approach this problem.

Some recognize loss-of-chance theories under particular circumstances.

Others require a more traditional showing of causation.

This is an important example of why causation doctrines cannot always be reduced to a single formula.

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Causation in Fact vs. Legal Causation

One of the most important distinctions in Tort Law is between factual causation and legal or proximate causation.

Factual causation asks:

Did the defendant’s conduct actually contribute to the injury?

Legal causation asks:

Is the connection between the defendant’s conduct and the injury sufficiently close and foreseeable for the defendant to be held legally responsible?

These are different questions.

A defendant’s conduct can be a factual cause without necessarily creating legal liability for every consequence that follows.

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An Example of the Difference

Suppose a driver negligently hits a pedestrian.

The pedestrian suffers a broken leg.

Because of the injury, the pedestrian misses an important business meeting.

The missed meeting causes the pedestrian to lose a valuable commercial opportunity.

The driver’s conduct may be a factual cause of the broken leg.

But whether every subsequent economic consequence is legally attributable to the driver is a separate question.

That is where proximate or legal causation becomes important.

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Factual Causation Is Usually the First Causation Question

A court generally cannot sensibly ask whether a consequence is legally attributable to the defendant until it has established an actual causal connection.

The sequence is therefore:

Did the defendant cause the injury in fact?

↓

If yes:

Is the injury legally attributable to the defendant?

The first question is factual causation.

The second is proximate or legal causation.

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Factual Causation and Foreseeability

Foreseeability is more strongly associated with proximate or legal causation, but it can also appear in discussions of the causal chain.

The important distinction is:

Factual causation is primarily about whether the defendant’s conduct actually produced or contributed to the injury.

Proximate causation concerns whether the law should treat that causal connection as sufficient for liability.

Keeping these questions separate prevents confusion.

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A Causal Chain

A useful model is:

Defendant’s conduct

↓

Risk created by conduct

↓

Intervening events

↓

Injury

↓

Damages

Factual causation asks whether the defendant’s conduct is actually part of the causal chain leading to the injury.

Legal causation then asks whether the chain is legally sufficient to impose responsibility.

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Intervening Events

An intervening event occurs after the defendant’s conduct but before the ultimate injury.

For example:

Defendant negligently creates danger

↓

Third party acts

↓

Plaintiff is injured

The third party’s conduct may or may not affect causation.

Some intervening events merely form part of the causal chain.

Others may be sufficiently independent or extraordinary to affect legal causation.

That distinction belongs primarily to the study of proximate cause.

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The Plaintiff’s Own Conduct

The plaintiff’s conduct can also complicate factual causation.

Suppose a defendant creates a dangerous condition.

The plaintiff then behaves carelessly.

The plaintiff is injured.

Both actions may contribute to the outcome.

The plaintiff’s conduct may affect:

• factual causation;
• comparative negligence;
• assumption of risk;
• or other doctrines,

depending on the jurisdiction and circumstances.

It is important not to assume that the plaintiff’s conduct automatically eliminates the defendant’s causal role.

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Factual Causation and Comparative Fault

Suppose:

• Defendant drives negligently;
• Plaintiff crosses the street while distracted;
• both contribute to the collision.

The defendant’s negligence may still be a factual cause.

The plaintiff’s own negligence may then reduce recovery under a comparative-fault system.

Thus:

A plaintiff’s contribution to an injury does not necessarily mean that the defendant was not a factual cause.

Causation and allocation of fault are related but distinct issues.

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Factual Causation and Damages

Causation must connect the defendant’s wrongful conduct to legally recognized harm.

A plaintiff cannot simply point to a breach and demand damages without establishing the necessary causal connection.

The causal analysis therefore connects:

Wrongful conduct

to

actual injury

to

legally recoverable damages

The precise damages rules are addressed separately in Tort Law.

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A Complete Example

Imagine a property owner knows that a staircase has a dangerously loose railing.

The owner does nothing.

A visitor uses the staircase.

The railing breaks.

The visitor falls and fractures a hip.

The analysis is:

Duty

The property owner owes the visitor an applicable duty of care.

Standard

Reasonable care requires appropriate precautions concerning foreseeable dangers.

Breach

The owner knew about the dangerous railing and failed to act.

Factual causation

If the owner had repaired the railing, the railing would not have broken and the visitor would not have fallen.

Therefore:

But for the owner’s failure to repair the railing, the injury would not have occurred.

Legal causation

The court must then determine whether the injury was sufficiently connected and foreseeable for legal responsibility.

Damages

The plaintiff suffered a physical injury and potentially other legally compensable losses.

This example shows exactly where factual causation fits.

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A No-Causation Example

Now change the facts.

The owner knows that the railing is loose but repairs it properly.

Two weeks later, the visitor walks down the stairs.

A sudden earthquake causes the visitor to fall.

The plaintiff is injured.

The owner may still have had a historical duty concerning the railing.

But if the railing played no role in the accident, the owner’s earlier conduct may not be a factual cause of the injury.

This is an important reminder:

A breach must actually connect to the harm claimed.

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Another Example: Medical Negligence

Suppose a physician negligently fails to diagnose a disease.

The patient later dies.

The plaintiff must establish more than the existence of medical negligence.

The plaintiff must establish the relevant causal connection between the failure to diagnose and the death.

If proper diagnosis and treatment would probably have extended the patient’s life or prevented death, factual causation may exist.

If the evidence shows that the disease would have caused the same outcome at the same time even with proper treatment, factual causation may be absent.

The exact legal test and evidentiary requirements depend on jurisdiction.

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Factual Causation Is Not Moral Blame

Causation should not be confused with moral responsibility.

A person may feel responsible for an event without being legally responsible.

Conversely, a person may be legally responsible even without intending the result.

Tort law requires a legally sufficient causal connection.

The question is not simply:

“Who feels responsible?”

It is:

“Did the defendant’s legally wrongful conduct actually cause the plaintiff’s legally recognized harm?”

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Factual Causation and the “Chain of Events”

Students often imagine causation as a single arrow:

Defendant → Injury

Real cases are rarely so simple.

The actual sequence may be:

Defendant’s conduct

↓

Dangerous condition

↓

Plaintiff’s response

↓

Third-party action

↓

Medical treatment

↓

Complication

↓

Final injury

The court may need to analyze every important stage.

Some events may preserve the causal connection.

Others may complicate or break it.

That is why causation is one of the most fact-intensive parts of Tort Law.

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A Practical Factual-Causation Test

When confronted with a negligence problem, use the following method.

Step 1: Identify the alleged breach

What exactly did the defendant do wrong?

Step 2: Identify the injury

What harm does the plaintiff claim?

Step 3: Reconstruct the sequence

What happened between the defendant’s conduct and the injury?

Step 4: Remove the defendant’s conduct

Imagine that the defendant had acted reasonably.

Step 5: Ask the but-for question

Would the injury still have occurred?

Step 6: Identify other causes

Were there:

• other negligent actors;
• natural events;
• preexisting conditions;
• plaintiff conduct;
• medical complications;
• or independent events?

Step 7: Determine whether the defendant’s conduct actually contributed

If the injury would not have occurred without the defendant’s conduct, factual causation is strongly supported.

Step 8: Move to legal causation

Once factual causation is established, ask whether the law should treat the defendant as legally responsible for the consequence.

That is the next stage of the analysis.

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Common Mistakes

Mistake 1: Assuming breach automatically means causation

It does not.

A defendant can breach a duty without causing the plaintiff’s injury.

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Mistake 2: Assuming injury automatically means causation

It does not.

The plaintiff must connect the injury to the defendant’s conduct.

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Mistake 3: Confusing factual and proximate causation

They are related but distinct.

Factual causation asks whether the defendant actually caused the injury.

Proximate causation asks whether the connection is legally sufficient for liability.

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Mistake 4: Assuming there can be only one cause

An injury can have multiple causes.

Several defendants may potentially contribute to the same harm.

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Mistake 5: Treating the but-for test as a universal solution

The but-for test is foundational but can become difficult in cases involving multiple sufficient causes or scientific uncertainty.

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Mistake 6: Ignoring preexisting conditions

A preexisting condition does not automatically eliminate causation.

The defendant’s conduct may aggravate or accelerate an existing problem.

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Mistake 7: Using hindsight

Causation requires reconstruction of what actually happened, not speculation based solely on the eventual outcome.

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Factual Causation vs. Proximate Causation

The distinction can be remembered this way:

Question	Type of Causation
Did the defendant’s conduct actually contribute to the injury?	Factual causation
Would the injury have occurred without the defendant’s conduct?	Factual causation
Was the defendant’s conduct part of the actual causal sequence?	Factual causation
Is the connection sufficiently close for legal responsibility?	Proximate/legal causation
Was the type of harm sufficiently foreseeable?	Often proximate/legal causation
Should liability extend to this consequence?	Proximate/legal causation

The first group asks:

Did it actually cause the harm?

The second asks:

Should the law hold the defendant responsible for that harm?

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Key Takeaways

• Factual causation establishes the actual connection between the defendant’s conduct and the plaintiff’s injury.
• It is a fundamental component of negligence.
• The traditional test is the but-for test.
• The central question is whether the injury would have occurred without the defendant’s wrongful conduct.
• Breach of duty does not automatically establish factual causation.
• An injury does not automatically establish factual causation.
• Multiple factors can contribute to the same injury.
• Multiple defendants can potentially be factual causes.
• Preexisting conditions can complicate causal analysis.
• The plaintiff’s own conduct can contribute to an injury without necessarily eliminating the defendant’s causal role.
• Medical malpractice often presents difficult factual-causation questions.
• Scientific uncertainty can make causation particularly difficult to prove.
• Civil cases generally use the applicable civil burden of proof, often preponderance of the evidence.
• The but-for test may be difficult to apply mechanically when multiple independent causes are each sufficient to produce the harm.
• Alternative causation doctrines may apply in particular circumstances.
• Factual causation should be distinguished from proximate or legal causation.
• Factual causation asks whether the defendant actually caused the injury.
• Proximate or legal causation asks whether the connection is sufficiently close for legal responsibility.
• Causation must connect the defendant’s breach to the plaintiff’s legally recognized harm.
• Factual causation is therefore the essential bridge between breach and injury.

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Frequently Asked Questions

What is factual causation in tort law?

Factual causation is the actual causal connection between the defendant’s wrongful conduct and the plaintiff’s injury.

What is the but-for test?

The but-for test asks whether the plaintiff would have suffered the injury if the defendant had not engaged in the allegedly wrongful conduct.

What does “but for” mean?

It means:

Without the defendant’s conduct, would the injury have occurred?

If the answer is no, the defendant’s conduct may be a factual cause.

Is factual causation the same as proximate cause?

No. Factual causation concerns whether the defendant actually caused the injury. Proximate or legal causation concerns whether the connection is sufficiently close for the law to impose liability.

Can there be more than one factual cause?

Yes. An injury can have multiple factual causes, including conduct by multiple defendants.

Can a defendant be negligent without causing an injury?

Yes. A defendant can breach a duty of care without being a factual cause of the plaintiff’s particular injury.

Does an injury prove factual causation?

No. The plaintiff must establish a causal connection between the defendant’s conduct and the injury.

What happens when the plaintiff already had a medical condition?

A preexisting condition does not necessarily defeat causation. The defendant’s conduct may aggravate, accelerate, or otherwise contribute to the plaintiff’s injury.

What if the injury would have happened anyway?

If the plaintiff’s injury would have occurred even without the defendant’s conduct, factual causation may be absent.

What if two defendants caused the same injury?

Both defendants may potentially be factual causes. The applicable jurisdiction’s rules determine how responsibility is analyzed and allocated.

Can a third party break factual causation?

A third party’s conduct may complicate the causal chain. Whether it affects legal responsibility is often more closely associated with proximate or legal causation.

Is causation always proved with scientific certainty?

No. Civil litigation often requires decisions based on probabilities and evidence rather than scientific certainty.

What standard of proof applies to factual causation?

In many civil cases, causation must be established by a preponderance of the evidence, meaning generally that the claimed causal connection is more likely than not. The exact rule can vary by jurisdiction and claim.

What is the difference between causation and damages?

Causation establishes that the defendant’s wrongful conduct produced the plaintiff’s legally relevant harm. Damages concern the losses for which the plaintiff may obtain legal compensation.

Why is factual causation important?

Without factual causation, a plaintiff generally cannot establish that the defendant’s breach produced the injury for which compensation is sought.

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Further Reading

For an authoritative general overview of causation in American Tort Law:

Cornell Law School — Legal Information Institute: Causation

For the general concept of negligence:

Cornell Law School — Legal Information Institute: Negligence

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Conclusion

Factual causation is the point at which negligence law asks the most basic causal question:

Did the defendant’s wrongful conduct actually cause the plaintiff’s injury?

The traditional answer begins with the but-for test.

Imagine that the defendant had acted reasonably.

Then ask:

Would the injury still have occurred?

If it would, the defendant’s conduct may not be a factual cause.

If it would not, factual causation may be established.

But real life is more complicated than a simple hypothetical.

Injuries can have multiple causes.

Several negligent actors may contribute to the same event.

Plaintiffs may have preexisting conditions.

Medical treatment may introduce additional complications.

Third parties may intervene.

Scientific evidence may establish probabilities rather than certainty.

For that reason, factual causation is sometimes one of the most difficult elements of negligence to prove.

Nevertheless, the basic principle remains clear.

The plaintiff must connect the defendant’s wrongful conduct to the actual injury.

This gives us an important distinction:

Duty asks whether the defendant owed an obligation.

Standard of care asks what reasonable conduct required.

Breach asks whether the defendant failed to meet that standard.

Factual causation asks whether that failure actually caused the injury.

But even that is not the end of causation.

A defendant’s conduct can be a factual cause of an injury without the law necessarily imposing responsibility for every consequence that follows.

The law therefore asks one additional question:

Is the causal connection sufficiently close and legally significant to make the defendant responsible for the plaintiff’s harm?

That is the problem of proximate cause and legal causation.