At common law in Illinois, if a person was bitten by a dog and suffered an injury, he could only recover for his damages if he could prove the dog had previously shown a disposition to "bite mankind," and that the dog's owner had notice of this disposition, such as knowledge that the dog had bitten someone before. Absent evidence of a dog's vicious propensities, he was presumed to be "tame, docile, and harmless." Additionally, the injured person could not recover for his injury if he knowingly approached the dangerous dog, or provoked him. The liability of the dog owner was through an act of negligence, and only if he harbored a "vicious dog". The burden of proof was on the injured person.