Not only are contracts written in natural language, they are about events in the natural world. The blockchain cannot know whether you delivered 100 bushels of

Not only are contracts written in natural language, they are about events in the natural world. The blockchain cannot know whether you delivered 100 bushels of corn to the counterparty, what the quality of the corn was, whether you were responsible for the damage to your car or somebody else, whether the house you built is up to code, or any of the thousands of other conditions that are the subjects of everyday contracts.