Book Review of Ignorance of Law

My review of Douglas Husak’s book Ignornance of Law: A philosophical inquiry has just been published in the journal Jurisprudence. You can find the review here – if you would like the full review sent via email just drop me a line at

Here is the first part of the review:

Douglas Husak’s book is an intelligent, wide-ranging exploration of the legal principle “ignorance of law is no excuse.” This principle is one of the few pieces of legal doctrine known by many regular folks, along with the criminal standard of proof “beyond a reasonable doubt.” Although I work on issues in criminal responsibility, I admit I had not thought much about the principle in the 20 years since law school. The traditional approach to the doctrine might be explained in this way: in some cases, ignorance of the law fails to excuse offenders from culpability because as a matter of policy we feel they ought to have known the law governing their behavior. Placing upon citizens the responsibility to know the law is good policy because it may increase both knowledge of law (by inspiring persons considering questionable action to investigate legal rules, etc.) and law-abiding behavior (by dissuading those who discover their possible act is illegal from acting). Although many believe the criminal law’s primary purpose is state-imposed backwards-looking “just deserts” for moral wrongs, the law also serves to accomplish forward-looking aims such as enhancing moral agency[1] and decreasing crime. From this perspective, the principle that ignorance of the law does not excuse contributes to rule of law and social order by encouraging awareness of legal rules.

Husak’s position on ignorance of law is sometimes difficult to discern amongst the detailed critique and commentary on competing views that occupy most of the first 100 pages. In the end, Husak bucks a forward-looking account of the principle and concludes that ignorance of the law – or more exactly, ignorance of the law related to ignorance of the morality underpinning the law – ought to serve as an excuse to criminal guilt in most cases. Further, he claims ignorance of law ought to excuse in the same way that that ignorance of an important fact regarding one’s crime excuses. That he is mistaken regarding an important fact about his crime matters to a defendant’s blameworthiness – e.g. if the defendant kills in self-defense, mistaking the toy gun their victim is carrying with a real gun. A person who honestly believes they are in immediate danger from an armed aggressor is less than fully blameworthy for killing that aggressor even if they were mistaken about the threat. Similarly, knowledge or ignorance that some act is morally wrong clearly matters to moral blameworthiness, says Husak: other things being equal, a person who is ignorant of the moral wrongness of her act is less blameworthy than someone who is aware that what she is doing is wrong.[2] Where ignorance of that an action violates a criminal law is related to ignorance regarding the morality of the act, a person is less than fully culpable.[3]

Mistakes of Law, Mistakes of Fact

To explore Husak’s position that mistakes of law and fact are importantly similar, let’s examine a classic mistake of fact case. Imagine a hunter, Tabitha – armed with the appropriate license and taking due care – goes on a hunt for brown bear in the woods. It is a dark, rainy morning, and Tabitha spots a bear 50 yards ahead partially hidden by a tree. Tabitha takes her shot; but when she walks up to her kill she realizes it was not a brown bear at all, but instead a local homeless man in a full-length fur coat he found in a charity shop.

Tabitha has made a tragic mistake of fact. Her mistake excuses her from responsibility for the death of the man because she did not possess the mental states required to be guilty of murder. Tabitha did commit a voluntary act that resulted in a death; however, she did not cause the death purposely, knowingly, or recklessly under circumstances manifesting extreme indifference to the value of human life (Model Penal Code § 210.2). Further, Tabitha’s mistake was reasonable, so she is not guilty under a negligence standard. A reasonable person in the same situation would have made the same mistake; thus, we cannot expect Tabitha to have known better or acted differently.[4]

Now imagine that another woman, Sheila, wrongly believes that a “castle law” exists in her state that allows her to apply deadly force to any trespasser on her property. Sheila also does not believe that killing trespassers is morally wrong: instead, she believes strongly that any person found on her property without permission knowingly risks their life. One day a homeless man wanders into her backyard and attempts to break into Sheila’s garage. She shoots him through the garage door, causing his death.

On Husak’s view Sheila is at least partially excused from criminal responsibility if her mistake of law is related to ignorance regarding whether her action is morally wrong. Husak claims law itself creates no moral duty to obey (although the way in which a law rests upon moral obligations may be complex; e.g. it may involve a promise to comply). An obligation to obey the law comes solely from the duty to obey the moral rules for which the criminal law acts as a surrogate. Thus to be fully responsible, says Husak, a defendant must know her behavior is morally wrongful, not illegal.[5] Because criminal law is a surrogate for moral rules, a misunderstanding of the criminal law can result in a misunderstanding of moral rules. Ignorance of the morality of an action makes a person relatively less responsible than a person who knows that their act is wrong.[6] Indeed, a person does not merit any blame for conduct he performs “in complete ignorance of propositions that play no role in rational calculation,” so if a defendant who is mistaken regarding the law is completely ignorant that his act is immoral, he is not culpable for the act.[7]

Sheila sincerely did not know the act of killing the intruder was wrong, thus she was ignorant with regard to both the illegality and immorality of her act. In this case, an understanding of the moral wrongness of the act could play no role in her decision to kill the homeless man. Sheila, and persons like her, “lack blame for [an act] because their deliberation or practical reasoning is unassailable from the standpoint of internal rationality.”[8] By her own lights, what Sheila did was morally correct. Husak’s position is that Tabitha’s ignorance regarding the fact that entity she shoots is a man, and not a bear, is relevantly similar to Sheila’s ignorance regarding the moral wrongness of her shooting of the trespasser. Both Tabitha and Sheila make an important mistake that is relevant to their blameworthiness. On Husak’s theory, neither woman should be held fully culpable for failing to act in accordance with beliefs required for criminal responsibility that they just do not possess.

[1] See Manuel Vargas, Building Better Beings: A theory of moral responsibility (Oxford University Press 2013) for an account of how forward-looking gains in moral agency might be grounded by back-ward looking assessments of responsibility.

[2] Douglas Husak, Ignorance of Law: A Philosophical Inquiry (Oxford University Press 2016) at 31.

[3] Ibid 97.

[4] Note that in my previous example of a person who mistakenly kills in self-defense because she thinks her victim has a gun, if the mistake is reasonable, her mistake also negates the requisite mens rea for murder, but via the justification of self-defense.

[5] Husak (n 3) 97.

[6] Ibid 22.

[7] Ibid 153.

[8] Ibid.


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