What is the test for the doctrine of “family purpose” in law?

In MacKay v. Weatherbie, Cowan C.J.T.D. referred to the “family purpose doctrine” that existed in some jurisdictions in the United States. He described this doctrine as follows: ...In order to warrant the application of the family purpose doctrine and impose liability on the owner for the negligent driving of a member of his family, the member of the family must have been using the car by permission or authority, either express or implied. “...it has been held that the doctrine applies only where the driver has general permission to use the vehicle, and does not apply as to a member of the family who obtains special permission on the occasion of each use”. p.92