Proximate Cause

What It Is

Proximate cause (sometimes called “legal cause”) means the defendant’s action was closely enough connected to your injury that it’s fair to hold them responsible. It’s not enough that the defendant did something wrong — their wrongful conduct must have foreseeably led to the specific harm you suffered.

In § 1983 cases, you must prove both that the defendant violated your constitutional rights and that the violation caused your damages. Proximate cause is the bridge between the two.

How It Differs From “But-For” Cause

There are two types of causation in law:

• But-for cause (cause in fact) — “But for the defendant’s action, would the injury have occurred?” This is a broad, factual test.
• Proximate cause — Was the harm a foreseeable result of the defendant’s action? This is a narrower, legal test that limits liability to consequences that aren’t too remote or unexpected.

You need both. An officer might be a but-for cause of your injury (if they hadn’t arrested you, you wouldn’t have been in jail), but if the actual harm was caused by an unforeseeable intervening event, proximate cause may be missing.

Proximate Cause in § 1983

The Supreme Court confirmed that § 1983 requires proximate cause, not just but-for cause. Courts will ask whether the constitutional violation was closely related to the injury you claim.

For example:

• An officer uses excessive force and breaks your arm → clear proximate cause for your medical bills and pain
• An officer makes a false arrest and you lose your job because you missed work → likely foreseeable, proximate cause exists
• An officer arrests you unlawfully, and three months later your car is repossessed → much harder to prove the arrest foreseeably caused the repo

Intervening Causes

A defendant may argue that something else broke the chain of causation — an “intervening” or “superseding” cause. If that intervening event was unforeseeable, it may cut off proximate cause. But if it was foreseeable, the original defendant is still liable.

Proximate Cause and Municipal Liability

In Monell claims against a city or county, you must show the municipality’s unconstitutional policy or custom was the “moving force” behind your injury — this is essentially a proximate cause requirement. A policy that has no real connection to the violation won’t support municipal liability.

Key Cases

• Monroe v. Pape, 365 U.S. 167 (1961) — Foundational § 1983 case establishing causation principles
• Mt. Healthy City School District v. Doyle, 429 U.S. 274 (1977) — Causation framework in § 1983 retaliation cases
• Monell v. Department of Social Services, 436 U.S. 658 (1978) — “Moving force” causation requirement for municipal liability