If a law is passed that contains a demonstrably false statement or assumption about the world, how is it generally interpreted?

For example, laws will often list a category of things, and then give examples of specific things in the category. It is easy for some of the examples not to be true members of the category. You might have a law that says "Only fish, such as pike, capybara, and perch, may be eaten on Fridays; animal meat is right out."

Does that make the capybara legally a "fish" for the purpose of that particular law? How would that affect courts trying to make determinations about what other things not specifically enumerated are (legal) fish?

Would an attorney be able to get any mileage out of the argument that the capybara is not in fact a fish, as noted by leading fish experts?

Can a law or part of a law be struck down not for being wrong but just for being false?

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    In California, bees are fish. Does that answer your question? nbcnews.com/think/opinion/… Commented Apr 10, 2023 at 13:32
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    That's definitely relevant.
    – interfect
    Commented Apr 10, 2023 at 13:37
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    You may wish to modify your example law to contain only one error, since fish are in fact animals.
    – Vaelus
    Commented Apr 11, 2023 at 12:16
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    @Vaelus Indeed, fish are animals; but depending on context, they are not meat.
    – kaya3
    Commented Apr 11, 2023 at 14:08
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    obligatory nitpick: taxonomically capybaras are fish, as are all birds, reptiles, amphibians and mammals including humans. This should also illustrate the problems with using those terms without further clarification as to which meaning of "fish" is actually used.
    – Chieron
    Commented Apr 11, 2023 at 14:14

4 Answers 4


Nix v. Hedden, 149 U.S. 304 (1893) is a famous "error of fact" case in the US. The situation was that there was an import tariff imposed on "vegetables in their natural state" brought in from outside the US, but not on "Fruits, green, ripe, or dried, not specially enumerated or provided for in this act" which were on a "free" list. Since imported tomatoes were taxed, it was said that tomatoes are fruits and not vegetables. The court ruled that for legal purposes the terms "vegetable" and "fruit" have their ordinary meaning, and are not held to a possibly variable scientific definition.

Definitions were read from Webster's Dictionary, Worcester's Dictionary and the Imperial Dictionary, and witnesses with decades of experience in the produce trade were called who testified as to whether the words had "any special meaning in trade or commerce, different from those read". Dictionary entries were read regarding the definition of the words pea, eggplant, cucumber, squash, pepper, potato, turnip, parsnip, cauliflower and so on.

The court reasoned as follows based on the evidence. First,

The passages cited from the dictionaries define the word ‘fruit’ as the seed of plaints, or that part of plaints which contains the seed, and especially the juicy, pulpy products of certain plants, covering and containing the seed. These definitions have no tendency to show that tomatoes are ‘fruit,’ as distinguished from ‘vegetables,’ in common speech, or within the meaning of the tariff act

and since the terms do not have a special meaning in trade or commerce, they must receive their ordinary meaning. Observe that "scientific definition" is not even a contender in this discussion. The court observed that "dictionaries are admitted, not as evidence, but only as aids to the memory and understanding of the court".

The crux of the ruling is the following observation:

Botanically speaking, tomatoes are the fruit of a vine, just as are cucumbers, squashes, beans, and peas. But in the common language of the people, whether sellers or consumers of provisions, all these are vegetables which are grown in kitchen gardens, and which, whether eaten cooked or raw, are, like potatoes, carrots, parsnips, turnips, beets, cauliflower, cabbage, celery, and lettuce, usually served at dinner in, with, or after the soup, fish, or meats which constitute the principal part of the repast, and not, like fruits generally, as dessert.

In other words, specialized scientific definitions are not assumed to underlie the use of words selected by lawmakers. If lawmakers list "fish, such as pike, capybara, and perch", then for purposes of that law and that law alone, capybara is defined to be a fish. Explicit redefinitions are fairly commonplace in writing laws, and lawmakers universally have the power to redefine words so that "and means or and or means and, as necessary".

An example of a deliberate statutory redefinition is the fact that a bee is a fish in California, for some purposes, see Almond v. Fish. In the Fish & Game Code, FGC §45,

“Fish” means a wild fish, mollusk, crustacean, invertebrate, amphibian, or part, spawn, or ovum of any of those animals

which means that worms and jellyfish, and insects, are legal fish. The Endangered Species Act §2062 then says

“Endangered species” means a native species or subspecies of a bird, mammal, fish, amphibian, reptile, or plant which is in serious danger of becoming extinct throughout all, or a significant portion, of its range due to one or more causes, including loss of habitat, change in habitat, overexploitation, predation, competition, or disease.

Notice that under an interpretation of the law that ignores the statutory redefinition in §45, invertebrates and a number of chordates would not be protected by law. The court notes that this was a deliberate action by the legislature in 1969, in that enrolled bill reports in support of this modification included the argument that

The expanded definition of fish will permit closer control and monitoring of the harvest of species such as starfish, sea urchins, sponges and worms, and the ... Commission will be authorized to make regulations deemed necessary for proper protection and management of these species

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    I realize that the misspelling "plaint" for "plant" is in your source, but your source is in error; the opinion used the correct spelling: tile.loc.gov/storage-services/service/ll/usrep/usrep149/…
    – phoog
    Commented Apr 10, 2023 at 20:59
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    You do not need the hypothetical capybara. In California, Honey Bees are fish. ref1 ref2 Commented Apr 11, 2023 at 12:58
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    @MindwinRememberMonica yes, that is mentioned in the answer: "“Fish” means a wild fish, mollusk, crustacean, invertebrate [...] which means that worms and jellyfish, and insects, are legal fish". Bees are insects, and insects are invertebrates, and since invertebrates are explicitly mentioned as "fish", that makes bees "fish".
    – terdon
    Commented Apr 11, 2023 at 16:33
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    It's surprising that they chose to interpret "a wild fish, mollusk, crustacean, invertebrate, amphibian" to mean all animals of those types (whether water dwelling or not). After all, when they classified a tomato as a vegetable, it was done based on the way people commonly classified it. A normal person would usually classify only the water dwelling versions of those animals as fish. There seems to be a lack of consistency here unless there were some reasons to believe that the legislature really meant all invertebrates.
    – user4574
    Commented Apr 11, 2023 at 16:54
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    The explanation is that previously, there were no protections for invertebrates, then the legislature expanded the existing law. Rather that hunt down all of the places where "fish" were mentioned in that law and replace it with some longer expression (and possibly make a mistake), they simply redefined "fish". They really did mean all invertebrates.
    – user6726
    Commented Apr 11, 2023 at 17:05

When a statute presents a general category and says that category "includes" some specific examples, those specific examples are deemed to belong to that category for the purpose of the statute.

Statutory definitions are also used to expand the usual scope of a word or expression, for example:

In this section,

"fish" includes shell fish, crustaceans, and marine mammals;


In these examples, the statutory definition enlarges the ordinary (or technical) meaning of the defined terms by including things that might normally be thought to fall outside their denotation.

(Ruth Sullivan, Statutory Interpretation, 3rd ed. (2016), p. 81)

And in the U.S. textualist context:

Individual statutes often contain definition sections giving ordinary words a limited or artificial meaning.

(Antonin Scalia & Bryan A. Garner, Reading Law: The Interpretation of Legal Texts)

But Ruth Sullivan notes, "statutory definitions do not necessarily lighten the interpreter's load. Many simply add to the ordinary or technical meaning of the defined term, which must still be determined in the usual way" (p. 82).

There are many other competing canons and principles of interpretation. The fact that an unexpected example is listed may be read to imply that the general category is actually broader than its common meaning would normally convey. One cannot answer interpretation questions in the abstract. In , the current approach to statutory interpretation is that:

Today there is only one principle or approach, namely, the words of an Act are to be read in their entire context and in their grammatical and ordinary sense harmoniously with the scheme of the Act, the object of the Act, and the intention of Parliament.

Rizzo & Rizzo Shoes Ltd. (Re), [1998] 1 S.C.R. 27 at para. 21

This approach has not been as universally accepted in the U.S., but given the inherent tensions between various canons of interpretation (same word–same meaning; expressio unius; etc.), it is similarly not possible to answer interpretive questions in the abstract. In all but the clearest cases (and even these would only be clear in context), to make any meaningful argument, one would need at least the full statute for examination.

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    How does this operate when the category is a phrase, rather than a word. If instead of "fish" we use "animals covered in scales", does that legally make the fur of a marine mamal "scales"?
    – interfect
    Commented Apr 10, 2023 at 13:49
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    @interfect "not possible to answer interpretive questions in the abstract" operates equally well whether the item to be interpreted is a single word or a phrase.
    – phoog
    Commented Apr 10, 2023 at 20:53
  • While it is true that law texts often explicitly give special definitions for certain terms, the question is probably more concerned with implicit wrong underlying premises. Commented Apr 11, 2023 at 11:59
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    @Jen Your answer is fine (and upvoted); I just wanted to point out a perceived different emphasis in the question. It is not hard to imagine what the legal consequences of a particular explicit definition are, even if it happens to differ from a dictionary definition -- after all, that's probably the very reason an explicit definition was given! It is more interesting to discuss the fallout of a law based on false presuppositions. E.g. imagine a law starting with "All mentally ill, including homosexuals, are to be ..." What would we do with that? Commented Apr 11, 2023 at 12:54
  • @interfect "animals covered in scales" excludes all of the scaleless fish.
    – RonJohn
    Commented Apr 11, 2023 at 13:55

Does that make the capybara legally a "fish" for the purpose of that particular law?


How would that affect courts trying to make determinations about what other things not specifically enumerated are (legal) fish?

They would do their best to find a general principle. You see something similar in the efforts of Jewish legal scholars trying to apply Biblical Kosher food requirements to situations not described in the Hebrew Bible with Talmudic arguments.

In Catholic Canon law (from which this particular example is drawn), which presents the same fish on Friday conundrum, they have a somewhat easier task, because the Pope is someone who has the capacity to resolve such questions in an absolutely authoritative manner even without coming up for a consensus reason for the distinction. Historically, what happened was this:

During Lent, many Catholics deny themselves earthly pleasures to honor Jesus's sacrifice. Abstaining from meat has nothing to do with animal rights; instead, it's supposed to be a break from an ingredient traditionally viewed as indulgent and luxurious. That's why beef, pork, and poultry are considered meat but fish isn't. Fish was thought of as a "simple" source of protein in the Middle Ages, whereas meat from land animals was considered rich and therefore more "sinful."

As is the case with the laws of most religions, Catholics have found creative ways around this rule over the centuries. Between the 16th and 18th centuries, a clergyman in Venezuela wrote to the Vatican asking if it was alright to eat capybaras during times of fasting. The South American rodents (the largest on Earth) are certainly not fish, but because they spend a lot of time swimming, the church decided to classify them as such. The Vatican has also made exceptions for other semi-aquatic mammals like beavers and muskrats. Reptiles that live in water, like turtles and alligators, qualify as fish during Lent as well.

In general, it is always possible to devise a rule that includes all outlier terms in a list, although in some cases that rule will be more contrived than in others.

For an example from non-religious law, the term "commodities" in which trading in future is regulated by the independent government agency known as the Commodity Futures Trading Commission (based in Chicago), includes all agricultural crops except onions. This is due to the Onion Futures Act of 1958 which was passed because there was a notorious incident in 1955 in which someone committed a massive market manipulation with the onion futures market that did massive harm to everyday people in the U.S. economy, even though, in principle, there is no good reason to regulate onion futures any differently from, for example, potato futures.

Similarly, even if two bottles of wine have contents that are chemically indistinguishable from each other (a client of mine is actually in the business of making exact chemical replicas of high priced wines using mass spectrometry and similar precision chemical tests) under U.S. law:

To be designated as a “California” wine, 100% of the grapes used in the wine must be grown in that state. To bear a viticultural area designation such as “Napa,” “Sonoma,” or “El Dorado County,” 85% or more of the grapes used must be grown in the designated area.

So, it makes a factual distinction that doesn't really exist in a meaningful way from the perspective of a wine consumer.

Would an attorney be able to get any mileage out of the argument that the capybara is not in fact a fish, as noted by leading fish experts?


The best the attorney could hope for would be that there is also a capybara fish which is not as well known as the capybara mammal. If that were the case, the attorney could argue that the reference was to the capybara fish and not to the capybara mammal. But, if that isn't the case, the attorney has no leg to stand on legally. And, if there is an argument like that to be made, the legislative history of a law or regulation, regulations interpreting a statute shortly after it was adopted, or long standing practice in interpreting a law since its inception that is never authoritatively included in an authoritative legal document, could clearly rule out that interpretation.

Can a law or part of a law be struck down not for being wrong but just for being false?

Not really.

In very rare instances, when the plain meaning of a law is absurd to the point of undermining the intent of the law expressed in other contexts the courts will interpret "and" to mean "or", or "shall" to mean "may", or "do X" to mean "don't do X" and will interpret it contrary to the plain reading on the grounds that it was a mere drafting error in the law. But this authority is virtually never used to invalidate a legal finding of fact.

Indeed, sometimes the law compels us to ignore certain facts.

For example, even if a parole eligibility model that included race as a factor was more accurate in predicting recidivism while on parole than the best available model that doesn't consider that factor, a parole eligibility model that considers race as a factor would be invalid as a matter of law.

Similarly, even if it is factually true that someone was in possession of illegal drugs, juries in a criminal prosecution for possession of those illegal drugs cannot consider that undisputedly true factual evidence if it was obtained in violation of the 4th Amendment.

The case of "fish" for the purpose of a particular law is much easier than that, however, because definitions can't be false by definition. There is no absolutely and universally true definition of any word. Instead, legal terms usually have multiple similar but not identical meanings.

The situation where a word has multiple meanings is called in linguistics and legal theory: polysemy.

Polysemy—the existence of multiple related meanings for the same word or phrase—is a frequent phenomenon in legal and lay language. Although polysemy sometimes arises by accident, it also can be strategic: framers of legal rules can advance private and public interests by assigning meanings to terms that are different from—though connected to—the meanings that those terms carry outside the law. Understanding the functions of polysemy can help us design more effective legal rules and can shed light on ways in which legal actors translate language into power.

Even if you are trying to conform to some meaningful and consistent concept in defining a legal term in a particular way, you can't really choose the correct definition until you know what the definition is seeking to distinguish from things outside the definition, i.e. the purpose of the law.

Definitions that don't match the most common sense of word in plain language are common in both legal statute and regulation drafting, and in contractual drafting.

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    @supercat Judgment calls like that are why we have judges. They also illustrate the fact that there is potentially lots of uncertainty lurking in most statutes that haven't been the subject of heavy appellate litigation.
    – ohwilleke
    Commented Apr 10, 2023 at 23:08
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    @supercat apart from being sloppily worded, your clause clearly refers only to gasoline powered variants of said categories of vehicles. It would possibly even exclude 2 stroke engines as those run on a mixture of gasoline and engine oil, and would definitely exclude diesel powered vehicles. Which is why actual clauses refer to "internal combustion engines", thus including all fuel types.
    – jwenting
    Commented Apr 11, 2023 at 6:30
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    @supercat Those laws actually exist for emissions regulations. (I worked with this up to around 2010.) If the law says "gasoline powered vehicles", it does refer to any vehicle which gets its motive power from a gasoline engine, and not to anything powered solely by electricity, diesel or other sources. (The laws are actually more specific, but you get the idea.) Those laws don't even specify a vehicle in some cases, only the engine type, so everything from chainsaws to Ferraris is covered. Hybrid vehicles and electric-only vehicles have their own definitions where the difference matters.
    – Graham
    Commented Apr 11, 2023 at 6:56
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    @supercat: The phrase you give allows two possible interpretations. "such as" may introduce either examples of "vehicles" or "gasoline powered vehicles". This grammatical ambiguity can be resolved by the observation that there are electrical vehicles such as (electrical) cars. Resolving grammatical ambiguity via real-world knowledge is so common that it generally doesn't need to be spelled out.
    – MSalters
    Commented Apr 11, 2023 at 9:00
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    @psmears Thanks. Fixed.
    – ohwilleke
    Commented Apr 11, 2023 at 17:56

Does that make the capybara legally a "fish" for the purpose of that particular law?


I actually just dealt with this issue on the municipal level. A project of mine was before the Planning Board proposing an objectionable vice use. Pursuant to the zoning conditions, such a use could not be situated within 1,000 feet of a public park.

Because of the proposed vice use there was some public outcry on the matter. In an effort to kill the project, members of the public focused upon a publicly accessible walking trail immediately behind the site which the general public perceived as being a public park. After all, it was a public walkway with various amenities to facilitate the public's use of the space for biking and walking. Testimony was provided by the public that police periodically patrol for loitering. From the perception of the general public, it was a park.

Unfortunately, the zoning ordinance lacked a definition for 'public park', so the matter was referred to the Zoning Board for an official interpretation and it was deemed to not be a public park for the following reasons:

  • The walking trail itself isn't actually public property, it's a private utility's right-of-way with an easement to permit the walking trail.
  • The zoning ordinance does have a definition for right-of-ways which was likely initially crafted imagining public roads in mind, but regardless is applicable for this site.
  • For the proposed use, the Township's Council needed to issue a letter approving the use at the specific location in order for a license to be issued prior to the Planning Board hearing (which the Council did). Given the conditional use requirements were set prior to the issuance of the letter, presumably, the Council did not perceive the walking trail as being a public park by virtue of them issuing the letter.

Ultimately, the project was approved, against the wishes of some members of the public who insist that the trail is a public park. Regardless, their perception of it being a park is irrelevant for the purposes of what it is legally defined as.

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