If the subject-matter1 or parties2 are identified by the contract with reasonable certainty, oral evidence is admissible to show the persons or things to which such description applies. So where certain wrecked steamboats were sold by description, location, and name, oral evidence is admissible to show that the names of two boats were reversed by mistake, and that the loca-tion and descriptions were correct.3 So if a person is described as one to whom a certain obligation is owing, oral evidence is admissible to show who such creditor is.4