Before defendant's act can be considered the proximate cause, it must be shown to be a but for cause.
"But for" cause -- an act or omission to act is the cause in fact of an injury when the injury would not have occurred but for the act.
- Applies where several circumstances combine to cause the injury.
- Other tests:
-- Substantial Factor Test
-- where several causes concur to bring about an injury, any one alone would have been sufficient to cause the injury, it is sufficient if the defendant's conduct was a substantial factor causing the injury
-- Alternative Causes Approach
-- plaintiff must prove that one of the plaintiffs' negligence caused the injury and then burden of proof shirts to defendants
, and each must show that his negligence is not the actual cause.