So Bob accuses Alice of stealing his horse. Alice accues Bob of lying slander.

They can't both be right. So one is innocent the other is guilty.

But according to the law they are both innocent until one is proven guilty.

So the law is in conflict with logic.

How can this be?

Another situation. One of two twins steals a chemical weapon which is caught on CCTV. We know one of the twins is guilty. But in this situation wouldn't the logical thing be to assume both are guilty and send them both to jail in order that the guilty one doesn't activate the chemical weapon?

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    Your second question would be a matter of national security overriding the law; this does happen, but Law.SE is not the place to discuss its merits and drawbacks. – Tim Lymington supports Monica Oct 15 at 21:29
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    As you pose your first scenario it is likely one will end up being found guilty, but until then we do not know which one it will be. During the proceedings they each get the benefit of the doubt. Not illogical at all besides being a very foundational part of democracy. – George White Oct 15 at 23:55
  • @George well it is kind of illogical. Such as when a woman accuses a man of sexual misconduct and the man accuses the woman of lying. Since we must assume both are innocent, we must "believe" both the woman's accusations, and also "believe" the man's innocence. It is impossible to believe contradictiory ideas however much we try! – zooby Oct 16 at 1:09
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    Although in actuality, one of them is guilty, in the eyes of the law (most countries) everyone is innocent until proved guilty. If someone was caught robbing a house, they would still be innocent until proven guilty in the eyes of the law, until they have their court date. How would you determine which one was guilty without having a court hearing to decide? – Smock Oct 16 at 8:25
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    @Smock is right, your question is using "factual guilty" and "legally guilty" interchangeably when they shouldn't be – User37849012643 Oct 16 at 9:15

You misunderstand the significance of the phrase "innocent until proven guilty." This is in part because you are not considering the entire phrase.

The full phrase is that an accused party is "presumed innocent until proven guilty." This does not mean that the accused is innocent, only that criminal procedure must take as its starting point that the accused did not commit the crime.

The major implication of the presumption, and indeed its original purpose, is that it places the burden of proof on the prosecution. This means that if a prosecutor asserts that you stole something, you do not have to prove that you did not. Rather, the prosecutor must prove that you did. The only reason to present evidence of your own is to rebut the prosecutor's evidence.

Another practical implication is that a decision to detain someone awaiting a criminal trial may not be based on the assumption that the accused committed the crime. On the other hand, that decision is not based on the assumption that the accused did not commit the crime. There is a presumption of innocence, but no assumption of innocence, and the government is not obliged before the person is convicted to treat the person as if there is no accusation or charge.

Wikipedia has a decent discussion.

If we modify your question accordingly, it becomes

How can two people be presumed innocent until proven guilty if their stories conflict?

Now the answer should be clear. The prosecutor must develop evidence that shows which one of the people has committed the crime. If the prosecutor cannot do that, neither person may be punished.


Guilt / innocence is not relevant here because nobody is being prosecuted for a crime. Bob might be liable for defamation per se, if he tweeted that Alice is a horse thief. B might sue A for taking his property, and A might sue B for a defamatory tweet. To win the suit, each party must prove that it is more likely than not that the defendant did the act in question (and that the act had the requisite characteristics). The outcome is a finding of liability (or its lack), not guilt.

Since the verdict is a probabilistic function from evidence presented, the evaluators of that evidence, and the rules of inference presented (i.e. "the law"), it is possible to find that Alice is found liable for theft and also that Bob is found liable for defamation. The cases involve separate trials – separate sets of jury instructions, separate juries, separate presentations of evidence, and the "packaging" provided by the attorneys on both sides. The theft jury X may find that Alice probably did steal the horse based on facts 1,4,9 and instructions 3,6,10. The defamation jury Y may find that Bob did defame Alice based on facts 2,4,11 and instructions 5,8,13. Given that truth is a defense against a defamation charge, we might surmise that jury Y concluded from the evidence and instructions presented to it that Alice did not steal the horse. Likewise, Alice could be found not liable for the purported theft and Bob could be found not liable for defamation: jury Y might disagree with jury's X's conclusion.

Since the law never requires an axiomatic proof that P is true, it is always imaginable that the system computes "Probably P" when in reality P is false. In a civil case, P has to be proven to be "more likely true than false", but for a criminal case, the evidence for P must be stronger, to the point that it is unreasonable to deny P (but still "logically possible").

  • That is interesting. Yes, both could also be found guilty. I mean logically, only one of them truly committed the crime. But one can't say "because one is innocent it means the other must be guilty" or vice versa.... And yet in some cases this is true, for example in small claims caught one party is found guilty and has to pay the innocent party money in a sense. – zooby Oct 16 at 1:06
  • Stealing a horse is a crime though, so that might be both civil and criminal. – Andy Oct 16 at 1:44
  • Independent of the civil issued between Bob and Alice, the government might opt to prosecute Alice. We can make this even more complicated, but I wouldn't advise it. This point is that "guilt" and "liability" are not the same, and they aren't the same as the fact of reality that A or B happened. – user6726 Oct 16 at 4:34

You are overthinking "innocent until proven guilty". All it means is that the prosecution has the burden of proof and all a defendant needs to do is create reasonable doubt (in a criminal trial). And your first example has one "charge" that would be a civil suit.


Consider a drug trial: you set out to show that drug A is better than drug B. The data is inconclusive (at 95% confidence) so you reject that proposition. Another drug trial is conducted to show that drug B is better than drug A. The data is also inconclusive (at 95% confidence) so you reject that proposition also.

This doesn't mean that drug A is both better and worse than B, it means that it may or may not be - with the evidence you have you can't tell the difference. In law the null hypothesis is that the person accused is innocent.


In your first example, one is guilty of something, but we do not know which one so our presumption of each (separately) being innocent, is logical. And it is an important part of the legal tradition that made its way from England to the U.S.


In your above example, Alice and Bob could both be innocent because the crimes accused are not binary possibilities (If Alice stole Horses, then Bob is lying. If Bob is Lying, Alice did not steal horses). Rather, it could be possible that Alice is stealing the horses and Bob is lying (but had a very lucky guess) or that Bob is not lying in that he thinks Alice is stealing horses because Alice was framed.

It's important to note that the Accusation that Bob is lying is only actionable if Bob knew he was lying and intended to accuse Alice for other reasons. If Bob sees Horses being stolen by a shadowy figure who he thinks is Alice, it's not a criminal offense to report this to police if it's discovered that Charlie is the real horse thief. It is only if Bob had knowledge that would allow him to know it was definitely not Alice at the time he said it. Without evidence of this fact, Bob is in effect saying "I think Alice stole the horses." which is factually true in that it is Bob's opinion that she committed the action, regardless of whether or not he was factually correct.

In your first example, the fact that one crime requires a proven intent (the defimation) and the other does not (stealing horses). In Alice's case, her guilt or innocence hinges on whether or not she stole horses. The Law does not care about if she did it out of greed or concern for the horses' well being. In Bob's case, his guilt or innocence hinges on whether he was making a good faith or bad faith accusation, not whether or not the accusation was correct.

In your second case, U.S. Jurisprudence holds that it is better that 100 guilty people go free than a single innocent man goes to jail. If the police have identical twins Tweedle-dee and Tweedle-dum as suspects for a crime committed by only one twin, but they cannot show which twin did the actual crime, then for the sake of the good twin, it is better to let the evil twin go free then to incarcerate the good twin for a crime he did not commit. Though even identical twins have distinguishing features (for example, one twin is slightly taller than the other, or one has a mole on his face). Even fingerprints on identical twins are not identical, so if the evil twin didn't hide his fingerprints it should turn up. Additionally, while criminal guilt must remove all doubt that the events happened any other way then what the prosecutor said, issuing of warrants only requires probable cause (you can get a warrant to search both twin's property based off the camera as there is a likely chance you'll find it in one of their possessions. Joint property will set us back to square one, however.). Additionally, in the United States, the danger of a chemical weapon being triggered would be an exigent circumstance that would permit a search and seizure without a warrant to be conducted (exigent circumstances exist where law enforcement enters a privately held property without a warrant because of a time critical need for entry. A Bomb threat or a little old lady crying for help that they can hear on scene are often cited example moments where the need to save lives trumps the property owners right to 4th amendment protections and any evidence of crimes found while going through the plain view search of the property is usually permitted at trial. So if an old lady has fallen and can't get up and cries for help, she can be charged if illicit drugs are clearly visible, even though the cops would not have known but for helping her in her distress). The cops searching for a chemical weapon in one of two twin's residences could rise to this level if we do not know their intent but know they have it. The government agency would likely compensate the good twin for the violation to the tune of repairing the damaged door and other property damaged in their search.

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