The Model Penal Code's Answer

As noted above, the Model Penal Code is not a law but a model that many legislatures have adopted in whole or in part. It includes definitions of substantive crimes such as burglary, and states sometimes adopt those definitions. It includes suggested grading. It includes definitions of defenses. It includes suggested defenses and even discussions of prison. 

But its most important aspect for our purposes is the proposed definition section for mens rea. You can find the entire MPC on Lexis and elsewhere. Feel free to skim the table of contents to get a general sense of its scope, and to jump to particular crimes. But we will focus on Section 2.02, available on Lexis--but note that the relevant portions of Section 2.02 appear below in any event.

The MPC is sometimes contrasted with the "common law" approach. This statement can be confusing. "Common law" is an ambiguous term that can mean, in different contexts, law we inherited from England in 1776, or ancient law that pre-dates English statutes before 1189. It can also refer to judge-made law as opposed to statutes. It can even mean American statutes that are old by some arbitrary measure, including even those before 1962. 

What people really mean when they distinguish the MPC from the common law is simply that before the MPC, states had a "traditional" approach, often statutory, that the MPC drew upon but then improved upon and rationalized. The "common law approach" is a way of saying the traditional approach to the extent it varies from the MPC. That formula does little, however, the help a student understand the content of this so-called common law.

This book will greatly simplify. We will distinguish between the MPC and the common law soley with respect to mens rea, and primarily with respect to terminology and interpretative approach. The MPC will be our default; later, we will see a few minor variations that the common law provides. 

For now, we need only understand that the MPC came to solve the particular problem sketched above, to provide a limited number of defined mens rea terms and to provide a global interpretative scheme for courts to know what mens rea term applies to a particular element. In fact, the MPC emphasizes the idea of breaking a statute up into its individual elements and considering what mens rea applies to each element.