Exclusion of oral evidence bars contradicting written instruments, subject to exceptions like fraud, separate agreements, and usages. When the terms of a written contract, grant, disposition of property, or any matter required to be in writing have been proved, oral evidence is not admissible to contradict, vary, add to, or subtract from those terms; however, exceptions permit proof of facts invalidating the document (such as fraud, illegality, want of execution, incapacity, failure of consideration, or mistake), separate consistent oral agreements, oral conditions precedent, subsequent oral rescission or modification except where writing or registration is required, usages and customs not repugnant to express terms, and evidence showing how the document's language relates to existing facts.