[3825]

Thank you. I guess cash currency isn't really property either. It is backed by the "full faith and credit" of the government so it is like a IOU that the government requires you to accept to settle existing debts.

[mikeash]

Cash is at least a concrete thing you possess, rather than an abstract idea whose sole purpose is to prevent other people from doing certain things.

Edit: additionally, cash doesn't expire, while patents only last two decades.