The Yale Law Journal

February 2022

Fitting the MPC into a Reasons-Responsiveness Conception of Subjective Culpability

Criminal Law

abstract. This Note compares the Purpose, Knowledge, Recklessness, and Negligence (PKRN) mens rea regime laid out in the Model Penal Code (MPC) and dominant in American criminal law with the “reasons-responsiveness” conception of culpability widespread among contemporary philosophers and criminal-law theorists. Whereas a PKRN picture of culpability sorts an agent’s culpability for an action according to whether the action was performed purposefully, knowingly, recklessly, or negligently, the reasons-responsiveness picture locates an agent’s culpability in the responsiveness of the agent’s reasoning capacities, which their actions evince. While many criminal-law theorists are cognizant of these different conceptions of culpability, most have assumed that the two pictures of culpability generally converge when it comes to the relative culpability judgments of actions performed purposefully, knowingly, recklessly, or negligently, so that even for those who reject an underlying PKRN conception of culpability in favor of an alternative reasons-responsiveness conception, a PKRN mens rea regime can still provide a roughly adequate system of culpability proxies.

In contrast, this Note argues that criminal-law theory has deeply underestimated the degree to which these conceptions are in tension with one another. If the reasons-responsiveness picture of culpability is correct, we should expect frequent cases of interhierarchical disagreement between the reasons-responsiveness picture and the MPC grading regime. That is, we should expect frequent cases where, for example, an agent who acts purposefully is less culpable than an agent who performs that same action recklessly or negligently. This result has both important normative and empirical consequences for the practice and study of substantive criminal law. In particular, this Note argues that if the reasons-responsiveness account of culpability is correct, then the MPC’s grading system will often fail to track offenders’ relative culpability and result in predictably disproportionate punishments not merely within but also across grades of crimes.

author. Yale Law School, J.D. expected 2023; Ph.D., University of California, Los Angeles, Philosophy. I’m grateful to the audience at the Yale Law & Philosophy Work-in-Progress Workshop, where an earlier version of this material was presented. Special thanks to Gideon Yaffe, Dan Kahan, Gabe Mendlow, Pamela Hieronymi, Kenneth Simons, Steve White, Lee-Ann Chae, Brian Hutler, Yuan Yuan, Pinchas Huberman, D Black, Joel Sati, and David Emer. I would also like to thank the editors at the Yale Law Journal, especially Thaddeus Talbot.


According to the familiar Purpose, Knowledge, Recklessness, and Negligence (PKRN) mens rea regime introduced in the American Law Institute’s Model Penal Code (MPC) in 1962 and now dominant in American criminal law,1 the criminal liability of an agent who commits some offense varies depending on whether the agent acted purposefully, knowledgeably, recklessly, or negligently with respect to the material elements of that offense.2 MPC section 2.02(1) establishes that for a person to be guilty of an offense, they must have at least one of these four culpable mental states.3

MPC section 2.02(5) establishes a weak ordering among the four mental states. For any given material element, each of the four PKRN mental states involves as much or more liability than the subsequent state.4 Where the severity of crimes is graded based on mens rea, this ordering hierarchy is typically used to establish the respective grades.5 If, for example, someone causes the death of another person (the material element of criminal homicide under MPC section 210.1), their criminal homicide will be classified as a murder if their action was purposeful. But they will typically be guilty merely of manslaughter, a lesser offense, if they were only reckless with respect to the victim’s death, and of the even less severe crime of negligent homicide if they were only negligent with respect to the victim’s death.6 That is, if they did not intend the death they caused (and so did not act purposefully under MPC section 2.02(a)), but merely believed there was some substantial probability that a death might result from their actions (and so acted recklessly under MPC section 2.02(c)), they will be considered less liable for that act, and so guilty of a lesser grade of offense and subject to lesser criminal penalties.

Influenced by historical mens rea distinctions from the old common-law homicide doctrine, the MPC does occasionally engage in more fine-grained parsing of mens rea in its analysis of criminal homicide than it does for other crimes, as with the addition of “reckless[ness] . . . manifesting extreme indifference to the value of human life”7 (equivalent to ordinary purpose or knowledge for the purposes of grading under MPC section 210.2(b)), and purpose “under the influence of extreme mental or emotional disturbance”8 (equivalent to ordinary recklessness for the purposes of grading under MPC section 210.3(b)). It also provides affirmative defenses that can function as full or partial shields to liability based on more finely grained features of the defendant’s subjective psychology.9 Still, despite the potential for such mitigating or aggravating factors to affect criminal liability on the margins, the PKRN hierarchy provides the backbone of the MPC’s model of criminal liability and ensures at least a weak ordinal sorting of criminal liability. Though a purposeful homicide, for example, may sometimes be treated similarly to particularly severe cases of reckless homicide, the offender who commits a purposeful homicide will never be held less liable than an offender who commits negligent criminal homicide, nor will a case of aggravated reckless homicide be treated as involving more liability than ordinary cases of purposeful homicide.10

Underlying the MPC grading regime appears to be a crucial normative commitment to (1) the view that an agent’s responsibility for some act, and hence their subjective culpability, is a function of the proximate mental states behind the act, and (2) a substantive view about which proximate subjective mental states are normatively worse (that is, make the agent more culpable) than others. The same agent performing the same act is more culpable if they intended the effect (purpose)11 than if the effect was foreseen but unintended (knowledge),12 even less culpable if merely a risk of the effect was foreseen (recklessness),13 and less culpable still if they unreasonably failed to foresee any risk of the effect at all (negligence).14 Call the conjunction of (1) and (2) the PKRN picture of subjective culpability. While this picture of subjective culpability provides the most straightforward explanation for the MPC’s mens rea hierarchy, it is rarely articulated explicitly, and even more rarely defended.15 Recent empirical work also calls into question the widespread assumption that the PKRN picture of subjective culpability maps onto the common-sense intuitions of the average lay juror.16

The MPC grading regime’s apparent reliance on the PKRN picture of subjective culpability is particularly problematic because that picture is widely rejected by most contemporary moral philosophers and criminal-law theorists who hold instead what might broadly be labeled a “reasons-responsiveness” conception of culpability.17 According to this reasons-responsiveness conception of culpability, an actor’s bad state of mind consists not in their intentions, purposes, knowledge, or negligence, but rather in the responsiveness of their reasoning capacities, which their actions (given their purposes, knowledge, recklessness, or negligence) evince.18

This Note compares the PKRN mens rea regime with the reasons-responsiveness conception of subjective culpability. While many criminal-law theorists are cognizant of these different conceptions of subjective culpability, criminal-law theory has deeply underestimated the degree to which these conceptions are in tension with one another, and so underappreciated the downstream normative consequences of these two different underlying pictures of subjective culpability for substantive criminal law.

This Note proceeds in three parts. Part I explains in more detail the reasons-responsiveness conception of culpability and draws out the tensions caused by contemporary criminal-law theory’s joint commitments to both a PKRN system of criminal liability and a reasons-responsiveness conception of criminal culpability.

Part II, the heart of this Note, argues that the degree of tension between these joint commitments has been underestimated. In particular, while criminal-law theorists have noted ways in which a reasons-responsiveness picture of subjective culpability may lead to more fine-grained distinctions of criminal responsibility than the PKRN picture, and so lead to what I call intrahierarchical differences in criminal responsibility for particular offenses, almost all theorists have assumed that the two pictures of subjective culpability generally converge when it comes to the general relative culpability judgments of actions performed purposefully, knowingly, recklessly, or negligently. These theorists therefore conclude that, even if we reject the PKRN picture of subjective culpability, we can still maintain the PKRN mens rea hierarchy as a sufficiently good culpability proxy to form the basis of a normatively justifiable criminal law.19

In contrast, Part II demonstrates that the reasons-responsiveness picture of subjective culpability leads not just to intrahierarchical differences—cases where the reasons-responsiveness picture attributes differing degrees of culpability to two similarly situated offenders with the same PKRN mens rea states—but to interhierarchical differences in culpability attribution as well. That is, for the same offense, the reasons-responsiveness picture will sometimes attribute more culpability to certain agents with a lesser mens rea state on the PKRN hierarchy, such as recklessness or negligence, than to someone with a higher mens rea state on the PKRN hierarchy, such as purpose. I argue that these cases of interhierarchical variance are not merely conceptually possible but are likely to be widespread in some of the most important cases of criminal homicide liability. I argue that we should expect cases of negligent or reckless criminal homicide—like that of Derek Chauvin’s second-degree manslaughter conviction for negligently causing the death of George Floyd20—which involve the least criminal liability in the MPC mens rea regime, to frequently involve substantially more culpability than the typical purposeful homicide, which subjects agents to the most liability on the MPC mens rea regime.21 This means that the shift from a reasons-responsiveness conception of culpability to the PKRN mens rea model involves not just a loss of information and so minor differences in the culpability of equally liable actors, but substantial and systematic mismatches between offenders’ culpability and criminal liability. In addition to these important normative results, I also show how closer attention to these interhierarchical differences can provide an alternative, and compelling, explanation for recent empirical results concerning experimental subjects’ sorting of traditional PKRN mens rea states that run counter to the MPC’s expectations.

Finally, Part III considers how we might amend the MPC to accommodate a reasons-responsiveness picture of culpability, in light of the existence of interhierarchical variance. While defending a particular proposal is not the primary purpose of this Note, the Note does attempt to show how much of the previous discussion of reform presupposed that no significant interhierarchical variance was possible, and to explain how the costs and consequences of various reform options change once the prevalence of such variance is acknowledged. I survey several possibilities, including abandoning the requirement that criminal liability be weakly proportional to culpability, fundamentally revising the MPC’s mens rea regime, abandoning criminal grading in favor of increased judicial sentencing discretion, and introducing a general “absence of ill will” affirmative defense. Despite shortcomings with each solution, I argue that the “absence of ill will” affirmative defense is the least problematic of the possible solutions.