What is the test for a master to be held liable for the actions of his servant?

And finally we have these cases, of which Boyle v. Smith [1906] 1 K.B. 432, 75 L.J.K.B. 282, is an illustration, where the attempts to fix liability upon the master for the act of his servant failed because the act complained of was not within the scope of the servant’s employment. And it seems to me that this test—the scope of the servant’s employment—is the first test to be applied to all these cases and to the case at bar. Unless this first essential element is found to exist, there is, in my opinion, no necessity to inquire further, because no guilt can be imputed to the master. If it is established, the next step is to ascertain whether the statute under review is of the class dealt with under the first group of cases, where mens rea on the part of the servant is not essential; if so, the master is liable in any event; if not, the case may still come within the rule of the second group, where the servant’s guilty intention will cast liability upon the master.