This lesson, which assumes basic understanding of the default rules of construction, introduces the concept of mistake under the Model Penal Code. It is fairly basic in its coverage. The lesson introduces the MPC approach to mistake and relates it to common law doctrines. Using sample statutes and scenarios, it shows the relationship between the required state of mind and mistake and demonstrates how reasonableness is not generally required in MPC analysis. It then covers the difficult concepts addressed in § 2.04(2) (guilt of lesser offenses where defendant makes a "culpable" mistake) and explores the policy underpinnings of this rule. At the conclusion of the lesson, students should have an understanding of how the MPC deals with claims of ignorance and mistake. The lesson provides a separate section of review/practice questions.