Which rule identifies proximate cause by determining whether the defendant's act was a significant factor in causing the harm?

• A. Substantial factor rule
• B. Foreseeability rule
• C. But-for rule
• D. Intervening act

Answer: (A)

The main idea here is whether the defendant’s conduct contributed in a real and substantial way to bringing about the harm. The substantial factor rule says that if the defendant’s act was a substantial factor in causing the injury, liability can attach even when other causes were also at work. This is especially important when more than one cause could have produced the harm, because each factor doesn’t have to be the only cause—just a material, significant one.

This approach differs from the but-for test, which asks whether the harm would have occurred had the defendant not acted. When multiple independent causes exist, the but-for test can fail to assign liability to someone whose conduct nevertheless played a significant role. The substantial factor rule focuses on the real influence of the defendant’s act rather than its necessity in isolation.

Foreseeability informs whether the result was a likely risk of the defendant’s conduct and helps decide whether the harm is within the scope of liability, but it doesn’t replace the substantial factor assessment as the test for proximate causation. An intervening act can also affect causation by potentially superseding the defendant’s role, but only after you’ve determined that the defendant’s act was a substantial factor in causing the injury.

So, identifying proximate cause by whether the defendant’s act was a significant factor aligns with the substantial factor rule.