Is it an out if the law a person is accused of breaking is ambiguous or in any way poorly written that an accused can be set free from it?

I cannot think that every law enacted are made equally. Sometimes laws can be rushed while some party has enough power to do so, without the necessary care and thought as to the precise practical implications of the law.

Surely, there must ways of dealing with poorly written laws when a person's future is at stake?

  • Alexander Hamilton said, "The rules of legal interpretation are rules of COMMONSENSE, adopted by the courts in the construction of the laws. The true test, therefore, of a just application of them is its conformity to the source from which they are derived." -Federalist No. 83 This was said on the subject of jury trials.
    – pygosceles
    Jan 17, 2023 at 16:58
  • You shouldn’t confuse this with just not knowing the details, though. Also, “it was 100 pages” or some such won’t help you either.
    – A.fm.
    Jan 18, 2023 at 18:07

4 Answers 4


This is known as the rule of lenity.

A common formulation of the rule of lenity is as follows: If a federal criminal statute is grievously ambiguous, then the statute should be interpreted in the criminal defendant's favor.

Importantly, the rule of lenity does not apply when a law merely contains some ambiguity or is difficult to decipher. As this Court has often said, the rule of lenity applies only when “ ‘after seizing everything from which aid can be derived,’ ” the statute is still grievously ambiguous. The rule “comes into operation at the end of the process of construing what Congress has expressed, not at the beginning as an overriding consideration of being lenient to wrongdoers.”

Kavanaugh J., concurring, in Wooden v. United States, 595 U.S. ___ (2022), citing Ocasio v. United States, 578 U.S. 282, 295, n. 8 (2016), internal citations removed.


If a law is not clear enough to let people know what is and what is not a violation, the law may be held to be void for "vagueness". But if it is clear that an act is a violation, even if some aspects of the law are unclear or ambiguous, that will not automatically be a defense for a person accused of breaking that law.

In some cases a court will add restrictions or clarifications to a law, and will treat it as if those had been included from the start. That may or may not create a defense for a particular accused. For example, a court may add that a certain action is only a crime if done "with intent to deceive". Other intent restrictions may also be added.

The outcome will depend on just what sort of ambiguity or careless drafting is involved, and how it affects the actual acts the accused did or is accused of doing.


Poor writing of law is never a basis for overturning a conviction. Hard-core ambiguity might be, in which case the "rule of lenity" may choose between possible interpretations of a clause. See US v. Universal C.I.T. Credit Corp., 344 U.S. 218

when choice has to be made between two readings of what conduct Congress has made a crime, it is appropriate, before we choose the harsher alternative, to require that Congress should have spoken in language that is clear and definite. We should not derive criminal outlawry from some ambiguous implication.

re-cited in a chain of rulings up to Dowling v. United States, 473 U.S. 207 and beyond. However, there is the case of US v. Yermian, 468 U.S. 63, there the defendant made a false statement in a job application, and was convicted of violating 18 USC 1001 which said (wording at the time of the crime)

whoever, in any matter within the jurisdiction of any department or agency of the United States knowingly and willfully falsifies, conceals, or covers up by any trick, scheme, or device a material fact or makes any fictitious, or fraudulent statements or representations, or makes or uses any false writing or document knowing the same to contain any false, fictitious, or fraudulent statement or entry

shall be punished.

Yermian knew that his statement (about convictions) was false, and contended that the prosecution had to prove both that he knew the falsity of the statement (the easy part) but also that the statement was made in a matter within the jurisdiction of the US. The job application was to a private company, who then submitted materials to the government to get a DoD security clearance, which he did not know.

The court decided that the "jurisdiction" clause was outside the scope of the adverb "knowingly. The court does not engage grammatical science to learn that the structure is ambiguous, they instead rebuff the lenity argument by appeal to other considerations. They conclude that

Any natural reading of §1001 establishes that the terms "knowingly and willfully" modify only the making of "false, fictitious or fraudulent statements," and not the predicate circumstance that those statements be made in a matter within the jurisdiction of a federal agency

which is to say, they believe that the interpretation where "knowingly" refers to both "in the jurisdiction" is not natural. Technical ambiguity is not enough, one has to establish likely ambiguity, that is, it is likely that a speaker of English would arrive at both interpretations. There is a related interpretive doctrine known as the "last antecedent rule" which says that a modifier only holds of the last (nearest) possible thing being modified. The courts long ago devised this "first thing preceding" rule to resolve rampant ambiguity (even so, the rule is invoked mainly as low-level support for a conclusion that was reached by other means). In Yermian's case, "knowingly" might modify jurisdiction (which precedes) or "false" which follows. I don't disagree with their naturalness judgment – the important thing to notice here is that this narrows the scope of "ambiguity" from "possible ambiguity" to "probable ambiguity".

Another important part of the court's reasoning is based on legislative history, derived from reading earlier versions of the law (which, incidentally, has been re-worded since Yermian) – the "legislative intent" of the Congresses as a whole from 1918 up to the version applied against Yermian does seem to indicate a desire to prevent defrauding the government and there is no direct evidence that Congress intended to limit prosecution to just cases where a person also knew that the statement was "in a matter in the jurisdiction of the US". The court's conclusion is that all a person has to know is that they are making a false statement – it does not matter if they know that the statement is or has become "in a matter in federal jurisdiction".

The minority in this case (Rehnquist, Stevens, Brennan, O'Conner) find the language to be ambiguous, but that only shows that the particular conclusion about language is credible to reasonable legal minds. As the dissent puts it,

Although "there is no errorless test for identifying or recognizing plain' or `unambiguous' language" in a statute, United States v. Turkette, supra, at 452 U. S. 580, the Court's reasoning here amounts to little more than simply pointing to the ambiguous phrases and proclaiming them clear. In my view, it is quite impossible to tell which phrases the terms "knowingly and willfully" modify, and the magic wand of ipse dixit does nothing to resolve that ambiguity.

Liparota v. US, 471 U.S. 419 presents a similar situation about ambiguous scope, regarding food stamp fraud, where the statute (7 USC 2024(b)(1)) identifies the criminal act as:

Whoever knowingly uses, transfers, acquires, alters, or possesses coupons or authorization cards in any manner not authorized by this chapter or the regulations issued pursuant to this chapter

shall be punished. Again, there is ambiguity in the scope of "knowingly" – do you just have to know that you transferred the goods, or do you have to also know that the manner of transfer was not in compliance with the regulations? In this case, the court decided that the scope of "knowingly" must also extend to the authorization clause. In the holding, the court declares that "requiring mens rea in this case is in keeping with the established principle that ambiguity concerning the ambit of criminal statutes should be resolved in favor of lenity" (majority opinion written by Brennan, one of the dissenters in Yermian, which is cited in Liparota).

This is a topic on which books have been written. There is still no clear disposition of actually ambiguous laws.


Does ambiguity in law go in favor of the defendant in a criminal case?

It can, but the verdict must be formed according to Constitutional law in order to have a reasonable possibility of full access to leniency.

Surely, there must ways of dealing with poorly written laws when a person's future is at stake?

There is a way of dealing with them:

Insist on a jury trial. The U.S. Constitution guarantees a jury trial in every criminal case. That way you have access to the common sense, conscience, and reasonable sympathies of your peers, rather than being judged summarily by a member of the political establishment. Judicial review of bad or poorly worded laws is vanishingly rare in the absence of jury trial, while jury nullification applies pressure on judges to review the law (Very few other things do).

Interestingly, all other answers so far ignore the Constitutionally specified modicum of arriving at a verdict in all criminal cases, which is jury trial. If you have access to a jury trial, you have access to common sense, which entails leniency whenever warranted. Relying on a court rule of lenity in the absence of a jury leads to a circular problem, in that you are left to rely on the mercy of the establishment charged with enforcing and adjudicating the same law that you question. What reasonable checks or balances exist in that environment? Too few.

Jury trial and jury nullification provide an incentive for judges to push back against ambiguous or overreaching laws: In the first place, it nullifies the judge's propensity to convict according to the law, however ill-constructed, and in the second place, defying the common sense of the masses will make a judge or prosecutor who insists on charging or convicting over bad laws look like an idiot or a tyrant, affecting their job security.

  • 4
    -1 "The U.S. Constitution guarantees a jury trial in every criminal case." This is not correct when a crime is not punishable by imprisonment or fines above a certain amount. "Judicial review of bad or poorly worded laws is vanishingly rare in the absence of jury trial." This uncited statement is, I believe, incorrect. Jan 13, 2023 at 22:08
  • Unfortunately, jury instructions often include a judge's description of what the statute requires, as opposed to the actual statutory text. If there's a difference between the instructions and statute which the judge insists is trifling, but which a defense believes may result in a jury that would acquit given the statute instead convicting given the illegitimate instructions, I don't know what options a defense would have to preserve the record so that an appeals court finding that the instructions were illegimate couldn't decide they weren't sufficiently erroneous to justify a new trial.
    – supercat
    Jan 14, 2023 at 17:33
  • @DavidSiegel The US Constitution explicitly states "The trial of all crimes shall be by jury" (Article III, Section 2, Clause 3). Those who refuse a defendant's right to jury trial in any criminal case are therefore derelict. Real world experience is sufficient to corroborate my claim. Judicial review is extremely rare nowadays relative to the number of cases where the law could (and should) be questioned. Most conspicuous in this trend is the complete absence of jury trials in most criminal cases. Judges in bench trials tend to avoid questioning the law and instead focus on prosecution.
    – pygosceles
    Jan 15, 2023 at 10:26
  • @supercat An application for a writ of habeas corpus should suffice to preserve any court records for appeal, including any questionable jury instructions, per 28 USC § 2245. The act alone of issuing an application for such a writ from a qualifying party under 28 USC § 2241 requires the judge to file a certificate setting forth the facts occurring at the trial, and renders them admissible as evidence. The writ need not be granted by the court in order to enjoin the deposition of these evidences and render them admissible; the hearing of a qualifying application alone is sufficient.
    – pygosceles
    Jan 15, 2023 at 10:45
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    @pygosceles: //Do you see how access to the common sense and conscience of a jury eliminates any quandary about fastidious fixation// I see how it would do so if judges would recognize such behavior as part of a jury's duty, and cease their efforts to ensure that juries are ignorant of such things.
    – supercat
    Jan 17, 2023 at 23:11

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