- Nov 21, 2018
Let me start at the beginning. Specifically, let's start in the first week of 1L year, when most law students are introduced to criminal law. Crimes, they learn, must include an actus reus—a guilty act. Crimes must also include mens rea—a guilty mind. For a crime to occur, the actus reus and mens rea must happen concurrently. That's been the traditional law of crimes going back to the common law hundreds of years ago.
Around the same time that 1Ls are learning this, they are also learning the modern arrangement that crimes are enacted by legislatures rather than courts. What is a crime is now up to legislatures, not judges. And this creates a problem. The traditional requirements of actus reus and mens rea are common law rules. Courts announced them hundreds of years ago in a time when courts largely defined what was a crime. When courts define what is a crime, the courts were saying, they will define them in ways that include a guilty act and guilty mind requirement.
But in the modern world, in which legislatures define what is a crime, the common law rules for what is a crime are no longer obviously binding. What matters today is the constitutional limits of crime definitions. In a modern system, legislatures can legislate in the zone of whatever the constitution allows. So that naturally raises a question: What are the constitutional limits of crime definition?
There is surprisingly little law answering that question. There is some, but not that much. That's surprising, I think, because the constitutional limits on crime definition are fundamentally important. But there's also a reason for the relative absence of caselaw. Legislatures enact lots of new crimes, but they usually use preexisting tools to get there. And when legislatures enact criminal laws that may on their face seem like significant departures from traditional approaches, courts construe the new laws to reflect traditional common law principles. [my emphasis]