Volokh points to a wonderful example of coming to the right decision with the wrong thinking.
A couple were injured when their car struck a cow. The owner of the cow had no insurance, so they filed a claim with their own insurance company for coverage under its uninsured motorist provision. The company refused to pay, so they sued. The trial court ruled against them, and they appealed.
The point of contention was whether a cow is a motor vehicle. The court cites the American Heritage Dictionary's definition: "a self-propelled, wheeled conveyance that does not run on rails" The court correctly observes that:
a cow is self-propelled, does not run on rails, and could be used as a
conveyance; however, there is no indication in the record that this particular
cow had wheels. Therefore, it was not a motor vehicle...
On this basis, buttressed by precedant to the effect that a horse is not a motor vehicle, it affirmed the decision of the Court of Common Pleas that the couple were not entitled to compensation.
I think that the Court of Appeals made the right decision, but for the wrong reasons. The American Heritage Dictionary's definition is wrong. On the one hand, it is not necessary for a vehicle to have wheels in order to be a motor vehicle. In my judgement, and I believe that of most people, vehicles such as snowmobiles, tanks, and bulldozers are motor vehicles even though they lack wheels. Furthermore, adding wheels to a cow would not make it a motor vehicle. On the other hand, not all self-propelled vehicles are motor vehicles. A sled is not a motor vehicle, even though it is self-propelled. What makes a vehicle a motor vehicle is, not surprisingly, its reliance on a motor. The reason that a cow is not a motor vehicle is that it has no motor.
(Obviously any post regarding a cow needs to be in purple. I instinctively did the same when I posted another reference recently.)