The big play isn't about ownership. It's about liability.
If you own the tractor and something bad happens, it's product liability. Our intuitions of responsibility go back to the Code of Hammurabi.
If a builder build a house for some one, and does not construct it properly, and the house which he built fall in and kill its owner, then that builder shall be put to death.
If you license the tractor, well that's not quite so intuitive and there's lots of room to argue over the terms of the license rather than the arguing over legal precedent.
The big play isn't about ownership. It's about liability.
If you own the tractor and something bad happens, it's product liability. Our intuitions of responsibility go back to the Code of Hammurabi.
If a builder build a house for some one, and does not construct it properly, and the house which he built fall in and kill its owner, then that builder shall be put to death.
If you license the tractor, well that's not quite so intuitive and there's lots of room to argue over the terms of the license rather than the arguing over legal precedent.