Intervening cause is an independent force that occurs after the defendant's act and is also an actual cause of the harm.
Whether or not an intervening cause breaks proximate causation is usually determined using a foreseeability test.
Factors used in determining if an intervening cause breaks the defendant's proximate causation are:
- How substantial the defendant's causal responsibility is to that of the intervening cause
- If insubstantial, unlikely to be foreseeable.
- Whether the intervening acts were "reasonably foreseeable"
- The defendant cannot escape liability if the intervening act was "reasonably foreseeable."
An intervening cause can either be responsive to or independent of the defendant's actions.
If the other factors do not make it clear, it is unlikely to be proximate cause, but a few miscellaneous factors can still be considered:
- Whether the intervening cause completes the specific consequences intended by the defendant
- Whether the defendant's "active force" has come to rest, causing apparent safety, before the intervening cause occurs
- Whether the intervening cause comprised direct and deliberate human intervention