It occurred to me the other day that (in America) I could write book claiming that soda cures cancer, and there would be no legal consequence to that—free speech. But if I sold soda and claimed that it cured cancer, I'm pretty sure that would be illegal.

So my (very broad) question is: When does it become illegal to lie—or to make wildly unsubstantiated claims—in American jurisprudence? Is there a single philosophical distinction that cuts across the law, or are there just piecemeal exceptions to “free speech” for things like libel, false medical claims, incitement to violence, etc.?

3 Answers 3


There are lots of times when it's illegal to lie. Among them:

  • impersonating a federal agent (18 USC 912)
  • lying to a federal agent (18 USC 1001);
  • health care fraud (18 USC 1035 and 1347);
  • mail fraud (18 USC 1341);
  • wire fraud (18 USC 1343);
  • perjury (18 USC 1623);
  • False Claims Act (31 USC 3729-33);
  • and libel and slander (common law).

But you're right that these laws are all at least theoretically in conflict with the First Amendment rule that "Congress shall make no law ... abridging the freedom of speech." So why are some of them upheld against a First Amendment challenge while others are struck down?

The Supreme Court explained its rationale a few years ago in U.S. v. Alvarez, 567 U.S. 709 (2012). That case dealt with a federal statute making it illegal to falsely claim that you had won any medal that Congress had authorized to be awarded to the armed forces. The federal government said that false speech had no value and therefore was not protected, pointing to cases upholding laws like the ones listed above where the Court had used similar descriptions.

But the Court rejected that argument, noting that the cases where it has upheld laws limiting false speech dealt with "defamation, fraud, or some other legally cognizable harm associated with a false statement":

In those decisions the falsity of the speech at issue was not irrelevant to our analysis, but neither was it determinative. The Court has never endorsed the categorical rule the Government advances: that false statements receive no First Amendment protection. Our prior decisions have not confronted a measure, like the Stolen Valor Act, that targets falsity and nothing more.

Even when considering some instances of defamation and fraud, moreover, the Court has been careful to instruct that falsity alone may not suffice to bring the speech outside the First Amendment. The statement must be a knowing or reckless falsehood.

So that sort of gives you an organizing principle. It's not really a philosophical distinction, and meeting it doesn't mean that the lie is illegal, just that it may be outlawed.

tl;dr: The First Amendment usually does not protect false statements when they are:

  • made knowingly; and
  • made with some corrupt purpose.
  • That's a great answer; perhaps it's unfair to challenge the tl;dr, but suppose I am maliciously spreading the lie that soda cures cancer—just because I'm evil and I want more people to die. In that case, is it simply that the government hasn't made a law to make that illegal, but that they could?
    – adam.baker
    Commented Apr 6, 2018 at 9:52
  • Yeah, I had a hard time trying to think of what adjective to use to describe the kind of intent you need to fall outside First Amendment protection. "Corrupt" covers the vast majority of it, but not all of it, and "corrupt" may not even always be correct. I could imagine a law that would outlaw that, but a court would probably spend more time evaluating how the law was written than what your exact purpose was. But yes, as long as you're not in the soda business, I think this is a statement that is not illegal but could be outlawed, if the law was written very narrowly.
    – bdb484
    Commented Apr 8, 2018 at 1:17
  • 1
    Just came across an article trying to break this down. Like me, they conclude that there isn't really any neat way to draw the line under the existing case law, but they offer some proposals, based on whether the lie causes harms or generates a benefit, and whether those costs are excessive in light of any potential benefits that might come from the lie: papers.ssrn.com/sol3/papers.cfm?abstract_id=3165654
    – bdb484
    Commented May 4, 2018 at 17:38
  • 1
    @adam.baker The trouble with banning that kind of malicious speech is that it depends on your motive. From outside your head we can't tell the difference. Also the principle of free speech depends on listeners being able to discriminate between lies and truth, and hence the truth is eventually found by consensus. Imperfect, but nobody has come up with anything better. Appointing a government watchdog to determine truth never ends well. Commented Nov 15, 2018 at 9:06
  • I would also mention that while you may not be breaking the law criminally, I find it highly likely that you would get sued in civil court, especially if there plaintiff had a reason to believe in your claim (like if you were a doctor or something).
    – pboss3010
    Commented Nov 15, 2018 at 13:13

In United States v. Stevens, a 2010 Supreme Court case that overturned a law outlawing animal cruelty videos, they listed the general categories of speech that are unprotected by the First Amendment. (I bolded the ones that seem relevant to lying in particular, and omitted the internal citations and quote marks to make it easier to read.)

From 1791 to the present, however, the First Amendment has permitted restrictions upon the content of speech in a few limited areas, and has never included a freedom to disregard these traditional limitations. These historic and traditional categories long familiar to the bar,--including obscenity, defamation, fraud, incitement, and speech integral to criminal conduct,--are well-defined and narrowly limited classes of speech, the prevention and punishment of which have never been thought to raise any Constitutional problem.

Of course, just because speech isn't protected by the First Amendment, doesn't mean there is actually a law making it illegal. The federal government has very aggressively passed laws making it illegal to lie to federal officials, for example, and most states have not done the same.

  • Is your answer that there is no single philosophical principle, or that there is (if there is, then what is it)?
    – user6726
    Commented Apr 5, 2018 at 4:25
  • I guess it depends whether you consider this to be a single philosophical principle. Maybe it would be, like, five principles?
    – D M
    Commented Apr 5, 2018 at 4:31
  • It is, however, a very limited number, and the Supreme Court made it clear in this case that they aren't interested in carving out any new First Amendment exceptions beyond those historical and traditional ones.
    – D M
    Commented Apr 5, 2018 at 4:37

That would be libel and could get you in trouble if you meet some really stringent "ifs". First, the soda company you accuse needs to prove that at the time of writing you either knew it was a lie, or did not care. Secondly, they have to prove you caused them actual damages to their product or image (since people don't want cancer, they would probably drink more soda if they honestly believed you). Finally, since the soda company is a public entity for the purposes of defamation law, they would have to prove that your actions were malicious... so if you claimed this in what is clearly a farcical literature or intended it to be, you're off the hook.

I put in "public entity" to point out that the rules change if the person was not a public entity at the time of the defamatory report. Lets say I'm a reporter and write an article describing Old Man Jenkins, a farmer who know one really knows, is stealing money from the bank and dressing up as a local supernatural monster known as The Creeper to scare away people from the crime scene. Since Mr. Jenkins is not known until I publish the story so his forced entry into the public stage is impugning his good character and calling down a gaggle of meddling kids and their dogs to his property, I can be sued for defamation by Mr. Jenkins and he would not have to prove malice intent on my part. This would become even more apparent when some Meddling Kids and their Dog trap the Creeper a bale of hay and pull off the mask, revealing it to be Mr. Caswell, the Bank manager.

It also gets tricky as you can only lie about facts, not beliefs. If your book says "I believe soda cures cancer" rather than "Soda kills cancer" you are not lying, as you do in fact believe that statement. In the U.S. you do have a right to express your own beliefs no matter how stupid they are.

Similarly, had I reported "Old Man Jenkins is suspected to be the Creeper" rather than "Mr. Jenkins is the Creeper" I also have not lied. Someone (me at the least) does suspect him of being the Creeper thus, the statement is true. On the flip side, suppose I report "Mr. Caswell is the Creeper and Bank Robber", prior to Caswell receiving a guilty verdict in a court of law, I am committing libel. Mr. Caswell is only accused of a crime, but is still innocent until proven guilty by jury. Yes... even if we have photographic evidence and a signed confession.

Finally, remember that J. Jonah Jamerson takes great umbrage at being accused of Slandering Spider-man in his paper. Because he never spoke those words. He libeled Spider-man because he printed those words.

  • "Yes... even if we have photographic evidence and a signed confession." - No. The burden is on Mr. Caswell to prove by a preponderance of the evidence that the allegedly libelous statement is, in fact, false. Falsely accusing someone of a crime is "libel per se", but that only means damages are assumed - it doesn't skip the "false" part.
    – D M
    Commented Apr 6, 2018 at 17:12
  • Of course, most journalists won't want to take a chance, since if you report on enough cases eventually the accused person WILL be innocent and you'll get burned. See en.wikipedia.org/wiki/Richard_Jewell#Libel_cases
    – D M
    Commented Apr 6, 2018 at 17:14
  • Again, if they reported that he definitely did it, and the jury did not find guilt because Meddling Kids and a Dog interfered in the chain of custody of the evidence to put reasonable doubt, then Caswell goes free... and can now sue the paper (not the reporter... he wants the money) then that's going to be a bad day.
    – hszmv
    Commented Apr 6, 2018 at 19:18
  • Being found not guilty is (obviously) good for Caswell, but being found not guilty is not proof that he didn't do it. If he wants to sue, the burden of proof is still on him that the statement was false. (But yes, the reporter is very likely to have a bad day; defending yourself competently in court is expensive.)
    – D M
    Commented Apr 6, 2018 at 23:55

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