Economics
The Parol Evidence Rule and Its Exceptions
Quick fact
The parol evidence rule is not about what evidence is inherently unreliable; it is a rule of contract law that excludes prior oral or written statements from altering the terms of a final written contract. It forces parties to put all important terms in writing at the time of signing.
Why this is interesting
You and a friend agree on a used car sale, sign a one-page contract, and later he swears you promised a free tank of gas. Can a judge hear that oral promise? The parol evidence rule says no—unless you can find an exception.