Yaffe “Mens Rea by the Numbers” Type 4 Critical Application

Kailey Houck
3 min readOct 6, 2020

Gideon Yaffe analyzes mens rea and its application to criminal law by applying a numerical argument to the discussion. To begin, I would like to define two legal terms essential to understanding Yaffe’s argument. “Actus reus” is defined as a guilty act, and “mens rea” is defined as the intention or knowledge of wrongdoing that constitutes part of a crime, as opposed to the action or conduct of the accused.”

Yaffe begins his explanation of the numerical argument by defining S as a strict liability act with actus reus elements E1, E2… (Yaffe 397) On the other hand, Yaffe defines S+ as a crime with exactly the same actus reus but with mens rea elements M. (Yaffe 397) The question becomes a discussion of whether a new statute would require mens rea for conviction, mirroring S+. Using a matrix, Yaffe concludes that “convicting without mens rea is equivalent, but not identical to, convicting the innocent.” (Yaffe 399) He follows by explaining Blackstone’s Ratio, which states that “10 guilty people going free has exactly the same disvalue as one innocent person being convicted, then we can construct an ordinal value function that could help us to determine, when coupled with some empirical information, whether the improvement in hit rate from the institution of the default mens rea provision outweighs the loss in increase in miss rate.” (Yaffe 399) Regarding the numerical argument, Yaffe argues that calculations are not simple, and even if Blackstone’s ratio is accepted, the new mens rea stature needs scrutiny.

Yaffe then follows by using an example to further scrutinize the new mens rea statute. Sex crimes with children, he argues, should not be criminalized under the new mens rea stature and should instead be considered under strict liability, or S. He argues that sex crimes with children falls into a special category where three things must be true: “(1) it must be wrongful in part because it causes harm, H, (2) false acquittal must cause harm, G, and (3) G and H must be closely enough related so that the crime is more wrongful in virtue of G.” (Yaffe 406) Sex crimes with children fall into this category because those who sexually exploit children do so by convincing their victims that there is nothing wrongful about their behavior. This leads victims to later become preparators, and acquittal reinforces the predator’s lie. Yaffe concludes that strict liability should be used to criminalize sex crimes with children instead of mens rea because ““the overall improvement through a regime that requires mens rea is not large enough to put us over the threshold in which we are permitted to be complicit in the special wrongdoing of those who commit such a crime and get away with it.” (Yaffe 407). In other words, the reason to favor S over S+ is that we shouldn’t be complicit in other people’s wrongdoing.

While Yaffe explains and argues how mens rea should not be used to criminalize sex crimes with children. I am curious how his argument would further apply to sex crimes involving children. Specifically, in my JOUR 303, we discussed the implications in minors creating, distributing, and having child pornography. I think this would be another example of something that falls in a special category that requires strict liability. While the ownership and distribution of child pornography is legally wrong, it does not require a wrongful intention or mindset. In addition, minors’ use of child pornography remains a controversial topic, especially as the minors in question get closer to becoming adults. I think Yaffe would agree that this case would also not qualify to be criminalized under the new mens rea statute, and should instead be considered under strict liability.

Yaffe, Gideon. “Mens Rea by the Numbers.” Criminal Law and Philosophy, vol. 12, no. 3, 2017, pp. 393–409., doi:10.1007/s11572–017–9430–0.