§ 24-3-8 [Parol Evidence to Show Void Writing]

If you sign a contract or other document, and something was wrong with it from the very beginning, you can use spoken or written statements from outside that document to prove the problem. Courts will allow this kind of outside evidence, even when the document itself looks valid on its face.

The same is true if a written agreement was fine at first but later became invalid for some reason. You are allowed to bring in outside proof to show that the document lost its legal force over time. This gives people a real way to challenge a written agreement that should not be enforced.