ABA Family Legal Guide

Contracts and Consumer Law

Introduction to Contracts

Limits to a Contract

If I enter into the contract under a mistaken impression, does that affect the contract's validity?

Probably not, if the other party didn't know about your mistake. This defense, unilateral mistake, is almost impossible to prove, even if the mistake is about the most important terms of the contract. If allowed liberally, it would lead to a lot of abuse. People would claim they made a mistake to get out of a contract they didn't like, even though they had no valid legal defense. Therefore, courts hardly ever permit such a defense—and even then, only in specialized business cases.