Anderson v. Minneapolis, St. P. & S. St. M. Ry. Co.
A forest fire started in a bog and was found to have been caused by the defendant's negligence. It burned a large area, merged with another forest fire of unknown origin, and then burned plaintiff's property.
Page 300, Paragraph 3–Page 301, Paragraph 1Jury was instructed to find for the defendant if the damage was caused by the other fire, but not if it was by that fire in combination with defendant's, based on whether defendant's fire was a substantial factor in the damage. Jury then found for the plaintiff.
Is a defendant liable for a fire when the fire merged with another fire before causing the damage?
The other fire would have done the damage regardless of whether or not it merged with defendant's, so defendant can't be liable for causing it.
: When two causes combine to cause damage and either alone would have caused the damage, both are liable as long as both were a substantial factor in causing the damage.
The liability would be split if both causes were known. There should still be someone liable for causing one fire that would have destroyed it even if the other would have as well.
The known defendant is liable for a fire that causes damage while merged with a fire of unknown origin.