Owner orally authorized Agent to sell his house. Agent completed a sale of the house to Buyer. When Buyer attempted to enforce the contract against Owner, Buyer was told that the contract was not...

Owner orally authorized Agent to sell his house. Agent completed a sale of the house to Buyer. When Buyer attempted to enforce the contract against Owner, Buyer was told that the contract was not enforceable because Owner’s agency relationship with Agent was not in writing. Must Owner have given Agent written authorization?