Why is causation so difficult to prove in personal injury?

Personal Injury - September 29, 2026 by Horwitz, Horwitz & Associates

Causation is hard to prove because negligence and injury aren’t enough on their own. You have to link the two, and the link is where the argument usually lives: the defense will often accept that you’re hurt and dispute that they caused it.

Sometimes the connection is obvious. Often it isn’t, because existing conditions, earlier injuries, the medical treatments in between, and time itself give the other side somewhere else to point. An Aurora personal injury lawyer can review the evidence and work out what that link will take.

What does causation mean in an injury case?

It’s the provable connection between the defendant’s actions and your harm. Every negligence claim starts with a duty of care and a breach of it, and causation is what ties that breach to the injury. Illinois calls it proximate cause.

Illinois Pattern Jury Instruction 15.01 is what a jury hears: proximate cause means “a cause that, in the natural or ordinary course of events, produced the plaintiff’s injury.” Where there’s evidence something else was responsible, the jury also hears it “need not be the only cause, nor the last or nearest cause.”

Take a car accident involving someone who already had a back problem. The question is whether the crash contributed to the injury they’re claiming for.

What does Illinois require you to prove, and how certain does it have to be?

The injured person carries the burden of proof, and the standard is lower than the one people know from criminal trials. Illinois asks a jury to decide whether each proposition is “more probably true than not true.” The pattern instruction deliberately avoids “preponderance” and “greater weight of the evidence,” on the view that those phrases are harder to follow.

So causation doesn’t have to be certain. It does have to clear more than possible, and evidence showing the defendant’s actions might have caused the injury won’t get there.

That’s work for the record as a whole. Medical records, photographs, witness accounts, diagnostic testing, and treatment notes each carry part of it, and a personal injury attorney reads them together.

How do pre-existing conditions complicate causation?

They hand the other side an alternative explanation. A pre-existing condition doesn’t bar a claim, and making an existing problem worse can itself be the injury.

Say you had occasional neck pain before a car accident, and afterward it’s constant and you’re in treatment you never needed. The insurer will argue those symptoms are the existing condition running its course.

Your medical history separates the two. Records from before and after document changes in symptoms, treatment, physical limitations, and diagnoses, and your doctors can say whether the crash made things worse. The question is usually how an accident changed a condition rather than whether it created one.

Why is causation hardest in medical malpractice cases?

Because the patient was already sick. In an ordinary injury case the plaintiff was fine until the defendant acted. In medical malpractice cases an underlying illness is doing its own damage, and the claim has to separate the harm the negligence caused from the harm the disease would have caused anyway.

A patient is treated for a serious condition and gets worse. That sequence alone isn’t a case. It requires a breach of duty by the medical professional, a departure from the standard of care, and it requires that breach to have caused the extra harm.

Illinois also gates the filing. Under 735 ILCS 5/2-622, the attorney must attach an affidavit saying a qualified health professional reviewed the records and wrote a report finding “a reasonable and meritorious cause” for the action. Failing to file it is grounds for dismissal, so a malpractice attorney lines that expert up before filing. Our firm’s Chicago medical malpractice lawyers work with medical experts on the standard of care and the causation requirements.

What role do medical records and expert testimony play?

Records build the timeline, and experts explain it. The records show which symptoms existed before, what changed after, when treatment began, and what doctors observed during recovery.

Expert witnesses matter when the medical question reaches past what a jury can work out unaided. A medical expert can explain how that kind of injury happens and whether the condition looks more consistent with the defendant’s actions than with some other cause. That is what expert testimony is for.

Worried your case is too complicated? Talk to Horwitz, Horwitz & Associates

A complicated medical history doesn’t mean you don’t have a case. It usually means the case requires a closer look at the records and at what changed after the accident.

Horwitz, Horwitz & Associates has represented injured people in Illinois for over 100 years and recovered more than $1 billion on their behalf. We can review your records and work out what it will take to prove causation. It works on a contingency fee basis, so you pay no attorney’s fees unless compensation is recovered. Call (800) 985-1819 or contact us online for a free consultation with a personal injury attorney.