In order for the government to legally prosecute, convict and punish someone, in most cases it must prove that the person committed the criminal act (known as actus reus) and that he or she committed that act with criminal intention (mens rea). There are a variety of terms used to describe mens rea, including moral blameworthiness, a guilty mind, an evil mind, conscious will, or willful action.

Mens rea is a foundational element of American jurisprudence. The U.S. Supreme Court made it quite clear in 2015 in Elonis v. United States that mens rea is what distinguishes wrongful conduct from otherwise innocent conduct. It determines whom we hold criminally responsible.

While the current focus of federal criminal justice reform is primarily on sentencing, mens rea has recently become linked to the bipartisan bill to overhaul the sentencing system tabled in Congress late last year. Commenting on the proposed sentencing legislation, House Judiciary Committee Chair Bob Goodlatte (R-VA) said earlier this month in an interview with The Atlantic that, “a deal that does not address [mens rea] is not going anywhere in the House of Representatives.”

The argument is gaining traction in the Senate as well: Senate Judicary Committee Chair Charles Grassley (R-IA) observed this week that “we don't have a great deal of time to reach a possible compromise” on the issue in order to win passage of the sentencing reform bill this session.

The particular concern Congress has with the current status of criminal intent law is the extent to which average citizens can possibly know all of the 5,000 or so federal crimes and 300,000 federal regulations. How can one “intend” to commit a crime if he is unaware that his behavior is criminal?

Congressional advocates of mens rea reform, backed by powerful Conservative supporters such as the Koch brothers, argue that the traditional phrase “ignorance of the law is no excuse” is no longer realistic. They want the government to have to prove that someone knowingly committed a crime before he can be convicted. Opponents argue that the benefits of such changes could disproportionately accrue to corporations and white-collar offenders.

Regardless of the merits of either argument, I believe the debate has so far sidestepped one of the more troubling impacts of mens rea on our justice system.

I agree that there is a valid question about whether citizens can be aware of all federal crimes. But the problem associated with mens rea is much broader than just the question of whether someone is “knowingly” breaking the law. My concern is with the psychological, neurological, psychiatric, and intellectual ability or capacity of many offenders to form the required criminal intent.

Criminal intent or criminal responsibility requires awareness, conscious will, volition, and rational decision making. There is a routine presumption, which is rarely challenged, that criminal offenders have the ability to form intent. I challenge that presumption.

Here is why.

Today, 40 percent of individuals in the U.S. criminal justice system (federal and state) have a diagnosable mental illness. Sixty percent of inmates in the nation's prisons have experienced at least one traumatic brain injury. Nearly 80 percent of justice-involved individuals have a substance abuse problem. The prevalence in the justice system of individuals with intellectual disabilities is three to five times what it is in the general population. There are substantial numbers of individuals in the justice system with neurodevelopmental and neurocognitive deficits and impairments.

Moreover, there's overwhelming evidence that many individuals with mental illness, addiction, neurodevelopmental deficiencies, and intellectual deficits lack the ability to form intent as it is defined in the law. How many lack this ability we don't really know, because we rarely inquire about intent. But the statistics cited above should raise serious questions about how we go about the business of criminal justice in the U.S.

In the vast majority of state and federal criminal convictions, the government rarely is required to prove intent. That's because the vast majority of criminal indictments (roughly 95 percent) are resolved through a plea agreement. If the offender agrees to the terms of the agreement, it's essentially a done deal. That puts prosecutors in charge of sorting out who is criminally responsible and who is not. At the end of the day, the vast majority are held responsible.

Mens rea is supposed to serve as a gatekeeper at the front door of the justice system, separating innocent from criminal behavior. The reality is that criminal intent is just not much of an issue under current criminal procedure. That in turn has significantly contributed to our incarceration problem by facilitating the punishment of more and more individuals.

It has also contributed to our recidivism problem.

When we punish mentally ill, addicted, intellectually disadvantaged and/or neurocognitively impaired individuals, we tend to return them to the free world in worse shape than when they came in. This is simply more grease for the revolving door.

So, how do we align the intent and reality of mens rea? First, we need to appreciate that mens rea is largely a clinical question. Prosecutors are lawyers—not psychologists or neuroscientists. We should expand the expertise involved in decisions about intent by requiring independent clinical assessment of individuals at the front end of the decision to prosecute.

Second, we need to revise the law of intent by developing alternatives to the simple categories we currently have of determining whether someone is criminally responsible or not. We need to provide options for holding individuals “responsible, ” while diverting them to intervention or treatment rather than just punishment.

This is not “get out of jail free.” Rather, it is an opportunity to divert some individuals who do bad things and utilize evidence-based strategies that have been shown to substantially reduce the likelihood of reoffending.

That is more just. It enhances public safety, and it saves money.

William R. Kelly is a professor of Sociology at the University of Texas at Austin, specializing in criminal justice policy. His first book on criminal justice reform, “Criminal Justice at the Crossroads: Transforming Crime and Punishment,” was published in May 2015 by Columbia University Press. His second book, entitled “The Future of Crime and Punishment: Smart Policies for Reducing Crime and Saving Money,” will be published in July by Rowman and Littlefield.