Ignorance of Law is no Excuse

Introduction

“Ignorance of the law is no excuse,” says an ancient legal nostrum.

The reason for it is simple enough: If ignorance could excuse any crime, then ignorance might excuse every crime. Rather than impose on the legal system the obligation to prove a defendant’s knowledge of the law — with the defendant’s incentive running in the opposite direction, toward ignorance of the law — the legal system assigns to itself no obligation in this regard. Upon which defendants find that they have an enormous incentive to know what the law is and to comport themselves accordingly.

This is not necessarily as crazy as it sounds. It doesn’t assume that the accused did know the law; no one knows all the laws. No one ever has. It simply says that ignorance doesn’t matter.

How can that be defensible? In the old days, it wasn’t so difficult. As Cicero wrote:

There is a true law, a right reason, conformable to nature, universal, unchangeable, eternal, whose commands urge us to duty, and whose prohibitions restrain us from evil… This law cannot be contradicted by any other law, and is not liable either to derogation or abrogation.

Neither the senate nor the people can give us any dispensation for not obeying this universal law of justice. It needs no other expositor and interpreter than our own conscience. It is not one thing at Rome and another at Athens; one thing today and another tomorrow; but in all times and nations this universal law must for ever reign, eternal and imperishable.

  

Everyone can know the universal law by use of right reason. And by means of living at Rome or Athens, say, a citizen could become habituated to local modes of conduct, and these would supply whatever content the natural law did not.

Much manmade law is merely customary, and this type of law is neither an instantiation of the natural law nor a violation of it. Still, though, some customs may be needed to facilitate commerce and peace.

To learn these customs, whenever an individual entered into a new line of work, or into any other new endeavour, we could expect that he would observe carefully the actions of others who were already engaged in it; in general, he would conform himself to their pattern. In the process he would come to appreciate the inner logic of being a rope maker at Athens, before he attempted to make and sell rope at Athens himself.

So while it is impossible for any individual, even a lawyer or a judge, to sit down and write out the entire law code, it could still be relatively defensible to hold individuals accountable for their violations of it. The law was an expression of two things that individuals ought to know, namely the universal law and the particulars of one’s own time and place.

But this is in a sense a house of cards: What if custom and the universal law conflict? Which one prevails?

Cicero says that it’s the custom that must give way, but it is not clear that it actually will give way in any particular instance. Bad customs can endure for centuries, sometimes.

Or what if the written law is ambiguous, as applied to a particular case? What if one law conflicts with another, or if there is a dispute over which part of a large customary legal code governs a particular circumstance? What if two parts of universal law appear to conflict with one another? Or if there is a question about which part of universal law is applicable in a particular case?

To resolve these types of conflicts is the work of a judiciary.

1. The Roman Experience

The ignorantia legis maxim is of ancient vintage, dating back at least as far as the days of the Roman Empire. Legal scholars have described the Roman maxim primarily as a concept of civil law, which was founded on the straightforward (if fictitious) rationale that the law was “certain and capable of being ascertained. “Thus, in litigation, positive proof of a citizen’s knowledge of the law’s requirements or proscriptions was not required. Rather, citizens were presumed to be familiar with the law, for it was not the function of the Roman law “to aid the fools."

Even from these early beginnings, however, application of the maxim was subject to important, if limited, exceptions when the law was not, in fact, definite and knowable. Despite widespread acceptance of the maxim, Roman law permitted certain groups of persons to claim ignorance of the law as a defense. The very young, for example, were considered to be incapable of comprehending important aspects of the law and thus were permitted to excuse their deviant behavior by claiming ignorance of the law’s requirements or restraints.

So too might disenfranchised women, soldiers away from home, and “peasants and other persons of small intelligence” escape penalty by claiming unfamiliarity with certain of the law’s commands. The common link between these disparate groups appears to be that they were all thought to lack some essential quality that would enable them to appraise or know the law, such as aptitude (women and members of the underclass), maturity (children) or notice of the law’s enactment (absent soldiers). Latitude for error was accorded these people so as not to penalize them for failing to meet legal obligations that were, to them, either unknown or unknowable.

The Roman reprieve extended only so far, however. Although these disparate groups of Roman citizens were considered to be incapable of knowing the ius civile (the body of civil law that governed Roman relations), they were expected to know and comply with the us gentium (the system of laws that “natural reason” had settled among all persons everywhere). As generously put much later by legal commentator John Austin, because these persons did not fall within the state of “general imbecility,” they could be expected to know the ius gentium, which was based on principles of natural reason presumptively understood by all.

2. The Maxim in England

In England, the maxim took on a less forgiving cast. Although it appears that the maxim originated in civil actions under Roman law, the English courts permitted it to control the outcome of criminal actions as well. In addition, the English common law courts defined the distinction between claims of ignorance or mistakes of law and mistakes of fact. Mistakes of pertinent fact were generally considered to provide a defense, while mistakes of law generally were not.

Early commentators on the English maxim defended it on the same rationale that the Romans had employed: the law was “definite and knowable” so it was fair to demand the compliance of anyone who possessed sufficient capacity to know it. While the very young and the mentally incompetent were afforded some latitude for error under this rationale, all other subjects of the realm were obligated to know the law, and presumed to do so. Later, however, as reflected by the passage at the start of this Article, British legal theorists began to offer utilitarian rationales for the principle—the fear that without the maxim the defense of ignorance of the law would be abused (all would claim ignorance to avoid punishment) and the concern that feigned claims would be impossible to refute.

Despite the English devotion to the ignorantia legis maxim, important (though limited) exceptions to the maxim existed under English law, just as they had under Roman law. One scholar noted: “In both [the Roman and English] systems considerations of equity induced the courts to deviate from the rule if arising cases did not expressly warrant its application.” Departures were also granted in criminal cases when the doctrine of mens rea required that they be, such as when particular specific intent crimes required proof of an intent that was negative by the accused’s lack of knowledge of his culpability. 

 

3. The Maxim in the United States

  

The ignorantia juris maxim currently in place in the United States grew out of this venerable ancestry. Broad and early acceptance of the maxim is found in numerous cases. As with the Roman and British versions, the American version of the principle was frequently articulated in lofty terms: every person “of reasonable understanding is presumed to know the law, and to act upon the rights which it confers or supports,” and “it is culpable negligence in him to do an act...and then to set up his ignorance of law as a defence.”

Legal theorists continued to study the maxim and proposed three additional rationales in its support. Rejecting Austin’s argument that problems of proof justified the maxim, Oliver Wendell Holmes proposed an alternative utilitarian rationale: “To admit the excuse at all would be to encourage ignorance where the law-maker has determined to make persons know and obey, and justice to the individual is rightly outweighed by the larger interests on the other side of the scales.” In Holmes’s view, punishing offenders who acted in ignorance of the law would achieve optimal societal knowledge of, and compliance with, the law. Thus, adherence to the maxim would promote a culture of legal literacy, while a retreat from it, even if in the interests of individuated justice, would give rise to a community of legal simpletons.

Professor Jerome Hall later challenged Holmes’s view and proposed that the maxim was justified by a more fundamental rationale—the rationale of legality. Hall contended that ignorance of the law claims could not be permitted for to do so would contradict the principle of legality, elevating offenders’ perceptions of the law above the law itself. Under the legality principle, when an accused fails to know that her conduct violates a law, whether because she failed to inform herself of the law’s existence or its application to her behaviour, or because she misunderstood or disagreed with its prescribed meaning, the law should be unforgiving.

Finally, Professor Henry M. Hart postulated that the “essential rationale” of the “much misunderstood” maxim is that any member of the community who engages in intrinsically wrongful, prohibited acts “without knowing that they are criminal is blameworthy, as much for his lack of knowledge as for his actual conduct.”

Using murder as an example of such an inherently wrongful act, Hart argued that even if an offender somehow lacked knowledge that the murderous act violated a specific criminal law, her conduct would still be blameworthy and deserving of criminal punishment as much because she did not know that murder was wrong as because she took another’s life.

Hart warned, however, that the maxim should only be applied to rules that adequately reflect community attitudes or needs; it should not be applied to an individual who offends a statute that punishes conduct that is malum prohibitum (conduct that is wrong only because it is illegal) rather than conduct that is malum in se (conduct that is intrinsically wrongful).

American courts have never agreed on a single rationale for the maxim. Some courts have applied the maxim to preclude mistake of law claims on the ground that such claims would arrest the administration of justice and provide a “shield for the guilty.”

Other jurists have cited the Holmesian view that the maxim is needed to promote knowledge and compliance with the law. Still others have espoused Hall’s principle of legality rationale, arguing that departures from the doctrine would undermine “core standards of criminal behavior” that the criminal law strives to secure. It is also not uncommon for combinations of the various rationales to appear in a single judicial opinion.

The inability of American jurists and commentators to agree on a single rationale for the maxim has not precluded its application in the United States, but it may help to explain the growing number of cases that have departed from the maxim over time. Notwithstanding the wide variety of rationales that have been used to support the application of the maxim in the United States, courts have also deviated from the maxim, just as their forebears had done, when evidence of bona fide ignorance or mistake has made criminal conviction (to them) unfathomable, or the law itself has required forgiveness of an accused’s legal error.

Thus, the courts have sometimes (though not uniformly) held that an accused’s ignorance of or mistake about a law is excusable if she fairly relied on some erroneous advice from an official responsible for interpreting or enforcing that law. Ignorance or mistakes of law might also be forgiven if it is determined that the accused reasonably relied on a statute or judicial precedent later repealed or overturned, or if the legislature failed to make the law adequately known or knowable.

An additional important subset of cases deviating from the maxim—and indeed, the cases with which this Article is primarily concerned—consists of decisions in which courts countenance ignorance or mistake of law claims because the claims disprove an element of the offense the prosecution is obligated to establish. These cases make clear that ignorance of the law will excuse if the law itself permits it to do so.

Put another way, the law itself may impose upon a prosecutor the obligation to prove an accused’s knowledge of the law as a specific element of a particular offense before a conviction may stand for its violation. For this reason, the statement “ignorance of the law does not excuse” is decidedly deceptive. A more precise statement of the maxim would be: “ignorance of the law is no defense unless the law under which an accused is prosecuted makes knowledge of the law an element of the offense.”

Determining when the law does this can be a formidable task. As a matter of democratic theory, because Congress, rather than the judiciary, makes the laws, Congress must decide whether an offender’s ignorance of the law will or will not provide a defense for each federal criminal enactment. When Congress makes its intentions clear, the task of interpreting the statute should be relatively straightforward. Problems arise when congressional intent is less evident. The less clear Congress’s intent, the more daunting the courts’ interpretive task becomes. In such situations, however, the maxim itself can be thought of as a helpful rule of construction that favors a particular outcome (that knowledge of illegality will not be an element) in the absence of evidence that Congress desired a different result.

4.  Ignorantia Legis

The inconsistencies in the judicial pronouncements regarding vagueness and intent, created by the struggle to prevent "unfair" convictions without abandoning the concept that ignorance of the law cannot excuse, do more than introduce disharmony into the theoretical structure of the criminal law. The inconsistencies also reduce the effectiveness of these doctrines in securing the fairness posited as their goal.

Both the doctrines and the goal of preventing unfair imposition of criminal liability would be aided by recognizing lack of knowledge of the law as a defense. The starting point must be acknowledgment that this is a separate defense, not a matter to be accomplished by creating special intent requirements for extraordinary cases. Indeed, the need for a defense of ignorance separate from the law of intent is largely the result of the difficulties faced by the Court with that area of the law since the advent of regulatory crimes.

At common law, the mens rea necessary to convict generally required that the government show the defendant to have acted purposefully to bring about a harm, to have known facts indicating that the harm would be a likely result of his action, or to have acted without concern for whether the harm would follow. The combinations of acts and harms to which these requirements applied were known by the community to be proscribed; under the M'Naghten rule, failure to appreciate the wrongfulness of one's act became the standard for insanity. 

Given common law crimes and intent requirements, Anglo-American courts thus found knowledge of the law to be unnecessary to guard against unfair criminal punishment. The rationales for and against igorantia legis, however, merit examination in light of the changed nature of crimes and of mens rea requirements.

5. The case against ignorantia legis

The case against ignorantia legis is rarely argued, though criticisms of the doctrine have been made by authors who support its retention. Along with such friendly criticism, discussions of related doctrines provide a basis for a critique of ignorantia legis.

Professor Packer, for example, objects to the refusal of the Court to require mens rea; his reasoning also could justify excusing by reason of ignorance. He found a consensus that punishment of conduct without reference to intent is "both inefficacious and unjust" because one who acts without "awareness of the factors making [his conduct] criminal" is not to be deterred by criminalizing such conduct, nor can he be held morally culpable." Similarly, it may be argued that punishing a defendant who acted in ignorance of the law is not likely to deter such conduct or to remove a socially dangerous individual from the public domain; nor is such punishment just-the defendant's ignorance does not mark his act as one properly calling for retribution.

The first basis for criticism of ignorantia legis, then, is the inefficacy of punishing the ignorant. Punishing persons who are not aware of the law making their conduct criminal has no direct deterrent effect."

The act for which such a defendant is punished could not have been deterred by the potential for punishment of which he was unaware. Nor will such punishment increase the ability of the law to deter him from repeating his illegal act. Having been informed of the illegality of his conduct when charged with a crime, the formerly ignorant offender will not be able to sustain a plea of ignorance as to future similar illegal acts.

His future conduct, thus, is shaped no differently by a law that punishes ignorant offenders than by one that excuses them. Punishing ignorant offenders nonetheless may have an indirect deterrent effect: the more persons punished, the more notorious the crime. It seems unlikely, however, that deterrence by notoriety would have much impact on commission of the relatively esoteric regulatory crimes of which ignorance most often is pleaded, and whatever deterrence is achieved must be weighed against its cost in deterring the regulated activity.

Irrespective of the balance between the benefit of the maxim in crimes prevented and its cost in socially desirable activities discouraged, ignorantia legis appears objectionable because it is unfair. The doctrine originally appears to have been a qualified maxim, compatible with common notions of fairness.

Roman law did not allow ignorance as a defense to actions under the ius gentium, the law derived from the common customs of the Italian tribes and thought to embody the basic rules of conduct any civilized person would deduce from proper reasoning. But ignorance of the more compendious and less common-sense ius civile was a defense allowed women, males less than 25 years old, soldiers, peasants, and persons of small intelligence. A defendant not otherwise exempted from the maxim's application apparently also was allowed a defense of ignorance of the ius civile if he had not had the opportunity to consult counsel familiar with the laws.

The English law adopted ignorantia legis without the qualifications that, under Roman law, tempered its harshness. Even so, for centuries the doctrine did not appear to produce unjust results.

 In Anglo-American civil law, damage to another individual generally is a prerequisite to the defendant's liability. If damage is not a formal element of liability, as in actions for trespass to land, an intangible damage has occurred by definition if the required elements are proved,"' and the award of "technical damages," to which plaintiffs are limited unless actual damage may be presumed or shown, hardly can be viewed as a stiff punishment.

The imposition of civil liability thus can be justified as compensating the victim for his loss; even if liability is not predicated on intent or negligence, the individual made chiefly liable may be viewed as less "innocent" than the person compensated, because the law of torts makes liable the person thought best able to avoid the harm.  As applied to Anglo-American civil law, therefore, ignorantia legis seems consistent with most rights of community members.

Until a century ago, the application of the maxim to criminal law also seemed fair, as a practical if not as a theoretical matter." Crimes initially were limited to a relatively few offenses that every sane person old enough to become a defendant reasonably could be presumed to know. Even as the number of offenses expanded, their basic nature remained the same and the protection of mens rea insured that noncompliance with the law was not punished unless both the actor's intent and his act were blameworthy.

Given this setting, the unquestioning acceptance of ignorantia legis by the foremost legal minds of the 18th and 19th centuries is not surprising. Nor is it surprising that as the criminal law increasingly came to be used as a sanction for various regulatory measures designed to advance social and economic policies that were connected only tangentially with community moral standards and as mens rea was abandoned for these crimes, authors made greater efforts to examine and to justify the doctrine. Because the criminal law is designed to enforce rules rather than to compensate victims and therefore may punish commission of an act even if no damage ensues, application of ignorantia legis to a wide variety of crimes now appears offensive to the standards of fairness embodied in civil law and expounded in discussions of other facets of criminal law.

A relatively clear standard of fairness has been espoused, for example, with regard to ex post facto laws, which impose or increase criminal sanctions for acts not punishable when committed or alter the evidence necessary for conviction.  An early objection to ignorantia legis was that it embodied the same unfairness as ex post facto laws, at least when applied to ignorance of "positive regulations, not taught by nature." ' An author surveying American customs and institutions and comparing them with their European counterparts wrote in 1792:

Where a man is ignorant of [a positive regulation], he is in the same situation as if the law did not exist. To read it to him from the tribunal, where he stands arraigned for the breach of it, is to him precisely the same thing as it would be to originate it at the time by the same tribunal for the express purpose of his condemnation.

In Shevlin-Carpenter Co. v. Minnesota, the Supreme Court rejected this analogy, declaring that "innocence cannot be asserted of an action which violates existing law, and ignorance of the law will not excuse. The law in controversy [punishing casual and involuntary trespass to state lands] has no ex post facto element or effect in it." 

Justice McKenna's majority opinion did not attempt to evaluate the impact of the ex post facto provision on ignorantia legis, but simply disposed of the analogy by noting that ex post facto cases dealt with laws enacted after an individual's action. The expansion of the ex post facto prohibition urged by the defendant would have conflicted with ignorantia legis; the opinion treated the latter maxim as though it were a constitutional mandate that had to be harmonized with the ex post facto clause and refused the expansion.

Certainly, more injustice derives from punishing a person for an offense that was not criminal at the time of his act than from punishing him when he was unaware of the act's illegality for another reason. Nonetheless, courts have recognized that it is unfair to penalize one who cannot reasonably be expected to know that his act is illegal, even if his ignorance is caused by something other than the nonexistence of the law at the moment of defendant's assertedly criminal act.'

Assessing a vagueness challenge, the Supreme Court noted that imposing criminal liability for violation of a statute that failed to define adequately the conduct it prohibited "would be like sanctioning the practice of Caligula who 'published the law, but it was written in a very small hand, and posted up in a corner, so that no one could make a copy of it.' In response to a defense of ignorance argued before a federal circuit court in 1810, it was held that sanctions could not be imposed for violation of a law passed before the violation, when no copy of the law had been received at the place where the act occurred until after the alleged offense."

Most decisions that define a standard of fairness for punishing persons unaware of the illegality of their actions do not involve the inaccessibility of the statute making the actions criminal. In cases in which the vagueness of a statute is alleged, criminal liability is not imposed for violation of an existing, accessible statute unless the statute gives "fair warning." ill Although decisions have not always been consistent with this rationale, perhaps as the result of the influence of the rationale used to support ignoratia legis, a number of cases clearly adhere to the principle that fair warning of the criminality of an act is required before the commission of the act is punishable."

In Lambert v. California, the fair warning requirement was extended beyond statutory specificity to include a reasonable likelihood that the defendant was aware that the law required some particular conduct."  The crux of the case against ignorantia legis thus is embodied in this question: If it is inconsistent with basic notions of fairness to penalize one for an act that, because of the nonexistence, inaccessibility, or vagueness of the law, the actor believed legal when done, why is it fair to punish one who is ignorant of the law for any other reason?

6. Ignorantia legis defended

Because the courts have seemed willing to accept ignorantia legis as a fixed star, the task of answering the question posed in opposition to the maxim has fallen largely to academicians. Legal scholars have defended punishing those ignorant of the law on numerous bases;"' from these, five major rationales appear.

Professor Austin argued that to investigate a person's knowledge or ignorance of the law in each case would hopelessly enmesh the courts in assessing virtually insoluble problems. Although fear of presenting difficult factual issues to courts may be a prime factor in continued judicial adherence to ignorantia legis, the argument was rejected firmly by Holmes nearly a century ago and no one has expressed much support for it since. Holmes "doubted whether a person's knowledge of the law is any harder to investigate than many questions which are gone into."  Considering the range of issues now put to judges or juries, particularly those relating to a defendant's state of mind when "specific intent" crimes are involved, it is difficult to quarrel with Holmes's observation.

The second major justification for ignorantia legis, advanced in Blackstone's Connnentaries and advocated most vigorously by Holmes, is that adherence to the maxim deters crime.  If ignorance excused, according to Blackstone, the law could be "eluded with impunity," or as Holmes put it, allowing a defense of ignorance would encourage ignorance of the laws. Application of ignorantia legis, however, cannot deter persons from repeating their offenses and can have only an indirect effect on deterring others. Holmes used robbery and murder as examples of crimes that should be discouraged for the good of the entire community; the community, he reasoned, must sacrifice the individual to the public goal of avoiding murder and robbery by punishing ignorant as well as knowing and intentional transgressors so that all may know these acts to be illegal.

Robbery and murder offer attractive examples, but ignorance of their criminality is virtually impossible. Ignorance is most likely to be pleaded to regulatory measures; examples, collected by Professor Perkins, of cases in which ignorance of the law was pleaded, and rejected, as a defense include operating a gaming device, betting on a horse race, conducting a raffle, and operating a saloon on election day after the close of the election. 

Although defendants may harbor mistaken beliefs as to what constitutes robbery or murder it is unlikely that any defendant would plead ignorance that these were criminal, excpt incident to a plea of insanity. If regulatory, rather than heinous, crimes are used as prototypes, the inadequacies of the deterrence rationale may be seen clearly. Convictions for these crimes are unlikely to receive the publicity accorded trials for murder, assault, embezzlement, and other crimes that appeal to the popular sense of adventure, so that ignorantia legis sacrifices the individual without educating, and hence without deterring, the public. Further, if less heinous crimes are involved, surely the balance between community and individual rights must be weighed more in favor of the individual. Embodied in the Constitution is the notion that fairness to individuals and orderliness in criminal proceedings are as much public desiderata as prevention of harm to persons and property.

The third justification for ignorantia legis is perhaps the best known and was the reason originally given in American criminal cases for adoption of the doctrine: all person are presumed to know the law. This presumption has been labelled "absurd," and seems to ignore common experience if applied generally. There undoubtedly are many crimes known to all competent, nonjuvenile members of society, but even lawyers are not aware of all federal crimes, much less of the multitude of state offenses. Beyond the illogic of such a presumption, there is no reason it should be exempted from the scrutiny the Supreme Court finds constitutionally mandated for other irrebuttable presumptions.

The Court in 1969 reaffirmed the rule of Tot v. United States that the validity of a presumption created by statute depends on a "rational connection between the facts proved and the ultimate fact presumed."  In Leary v. United States, the Court reversed a conviction obtained by use of a presumption that possessors of marijuana knew the marijuana to have been imported. The Court was unable to say "with substantial assurance that the presumed fact is more likely than not to flow from the proved fact on which it is made to depend."  If the basis for ignorantia legis is the presumption that anyone who commits a crime knows of the law he violated, that presumption should be tested in each case by the standard of Tot and Leary. Use of the presumption when it fails to satisfy that standard would violate due process.

Another rationale relied on to support punishment of persons ignorant of the law is that such ignorance is blameworthy in itself. Holmes rejected this thesis, noting that if it were the rationale for ignorantia legis a nonsensical result would be achieved: failure to learn the law would be punished as severely as failure to obey it.

Yet, after examining other justifications for the doctrine, it is this argument for ignorantia legis that seems most plausible. Holmes's objection to this rationale assumes an incorrect factual predicate. Failure to know the law is not punished unless it leads to a violation of the law; this coincidence, not mere ignorance, is punished to the same extent as knowing and wilful violation of the law. If ignorance of the law does not excuse because it is blameworthy, the judge or jury in each case should ask whether the particular ignorance claimed by a defendant is in fact blameworthy.

This determination should not present any inordinate difficulties; the usual question to be resolved would be whether a reasonable, prudent member of the community of average intelligence would, be aware of the violated law. If defendants were engaged in some regulated occupation and charged with violation of a law regulating that occupation, a more rigorous test would be applied: the fact-finder would determine whether the reasonable, prudent practitioner of that -occupation would have known the law. As presently applied, however, ignorantia legis makes no allowance for the possibility that ignorance of the law is not always blameworthy. In light of the nature of crimes of which ignorance is pleaded, the possibility that some ignorance may be culpable cannot justify the maxim's application in so many cases where ignorance is likely to be blameless.

A final support for ignorantia legis, offered by Jerome Hall, is more concerned with mistake of law than with ignorance of it.  Although Hall found the origin of ignorantia legis in the Roman notion that law is definite and knowable,' he argued that defense of the doctrine must rest on the unavoidable vagueness of the law. 

Courts have been designated as law declarers. If defendants' mistaken beliefs about the lawfulness of certain conduct exempted the defendants from criminal liability, Hall said, the function of the courts as law declarers would be destroyed and the law would become what anyone thought it was.  Hall's fear seems exaggerated. By exempting a defendant from punishment on the ground that he operated under a mistaken belief as to the law, courts would not abdicate their role in interpreting the law any more than they do by excepting from punishment one who acted under an impression of the law sufficiently far from correct to render the defendant insane.

In either case, the court declares what the law is but also declares that the defendant is not criminally liable for violating it. The court thus remains law-declarer in theory; allowing mistake of law to excuse will not impair the law-declaring function of the courts in practice unless it impairs obedience to the law declared. If allowing ignorance of a law to excuse would not lessen the deterrent effect of the law, then allowing a mistaken belief concerning the meaning of a law to excuse should have no greater adverse effect.

Further, if a mistaken belief of law is blameworthy, in that the average community member or professional would have learned the meaning of the law, the erroneous belief should not excuse criminal conduct even if ignorantia legis is narrowed to reflect its proper basis.  A requirement that mistake not be blameworthy substantially limits the number of cases in which mistake could excuse.

Certainly a professional knowing of the existence of a law concerning his profession might be thought adequately forewarned to find out its meaning and, if that meaning is unclear, to regulate his actions so as to avoid possible illegality. When the defendant claiming mistake of law knows of the existence and basic meaning of the statute but allegedly believes his conduct did not violate the law, the doctrine of ignorantia legis could not be used to convict him, nor would limiting that doctrine absolve him of liability. Unless his belief negated a required intent, the defendant will be held to answer for his act; if he acted voluntarily with knowledge of the law and that act is found to violate the law, the defendant's intent to violate the law could be inferred. Hall's argument, that allowing mistake of law to excuse would destroy the legal system, thus does not support ignorantia legis.

Bibliography:

Ignorance of the Law: A Maxim Reexamined. Ronald A. Cass

The Jurisprudence of wilfulness: An evolving theory of excusable ignorance. Sharon L. Davies

Nonpayment of taxes: When ignorance of the law is an excuse. Jon Strauss

The Death of a Maxim: Ignorance of Law is no Excuse (Killed by Money, Guns and a Little Sex) Mark D. Yochum