It may be clear that the person causing an injury is the agent of another. But a principal cannot be responsible for every act of an agent. If an employee is following the letter of his instructions, it will be easy to determine liability. But suppose an agent deviates in some way from his job. The classic test of liability was set forth in an 1833 English case, Joel v. Morrison. 1 The plaintiff was run over on a highway by a speeding cart and horse. The driver was the employee of another, and inside was a fellow employee. There was no question that the driver had acted carelessly, but what he and his fellow employee were doing on the road where the plaintiff was injured was disputed. For weeks before and after the accident, the cart had never been driven in the vicinity in which the plaintiff was walking, nor did it have any business there. The suggestion was that the employees might have gone out of their way for their own purposes. As the great English jurist Baron Parke put it, “If the servants, being on their master’s business, took a detour to call upon a friend, the master will be responsible.…But if he was going on a frolic of his own, without being at all on his master’s business, the master will not be liable.” In applying this test, the court held the employer liable.
The test is thus one of degree, and it is not always easy to decide when a detour has become so great as to be transformed into a frolic. For a time, a rather mechanical rule was invoked to aid in making the decision. The courts looked to the servant’s purposes in “detouring.” If the servant’s mind was fixed on accomplishing his own purposes, then the detour was held to be outside the scope of employment; hence the tort was not imputed to the master. But if the servant also intended to accomplish his master’s purposes during his departure from the letter of his assignment, or if he committed the wrong while returning to his master’s task after the completion of his frolic, then the tort was held to be within the scope of employment.
This test is not always easy to apply. If a hungry deliveryman stops at a restaurant outside the normal lunch hour, intending to continue to his next delivery after eating, he is within the scope of employment. But suppose he decides to take the truck home that evening, in violation of rules, in order to get an early start the next morning. Suppose he decides to stop by the beach, which is far away from his route. Does it make a difference if the employer knows that his deliverymen do this?