To this point, we have considered principles of liability that in some sense depend upon the “fault” of the tortfeasor. This fault is not synonymous with moral blame.
Aside from acts intended to harm, the fault lies in a failure to live up to a standard of reasonableness or due care. But this is not the only basis for tort liability. Innocent mistakes can be a sufficient basis. As we have already seen, someone who unknowingly trespasses on another’s property is liable for the damage that he does, even if he has a reasonable belief that the land is his. And it has long been held that someone who engages in ultrahazardous (or sometimes, abnormally dangerous) activities is liable for damage that he causes, even though he has taken every possible precaution to avoid harm to someone else.
Likewise, the owner of animals that escape from their pastures or homes and damage neighboring property may be liable, even if the reason for their escape was beyond the power of the owner to stop (e.g., a fire started by lightning that burns open a barn door). In such cases, the courts invoke the principle of strict liability, or, as it is sometimes called, liability without fault. The reason for the rule is explained in Klein v. Pyrodyne Corporation (Cases ).