When people disagree on controversial issues it is not uncommon for one person to accuse another of lying. In some cases, this accusation is warranted and in others it is not. There is also some confusion about what should count as a lie.
While this might seem mere semantics, the distinction between what is a lie and what is not a lie matters. The main reason for this is that to accuse a person of lying is to make a moral charge against them. It is not merely to claim that the person is in error but to claim that they are doing something morally wrong. While some people do use “lie” interchangeably with “untruth”, there is a difference. To use an easy and obvious example, imagine a student who is asked which year the United States dropped an atomic bomb on Hiroshima. The student thinks it was in 1944 and writes that down. She has made an untrue claim, but it would be unfair to accuse her of lying.
Now, imagine that one student, Sally, is asking another student, Jane, about when the United States bombed Hiroshima. Jane does not like Sally and wants her to fail, so she tells her 1944, though she knows it was 1945. If Sally tells another student that it was 1944 and puts that down on her test, Sally could not fairly be accused of lying. Jane, however, lied. While Sally is saying and writing something untrue, she believes the claim and is not acting with malicious intent. In contrast, Jane believes she is saying something untrue and is acting from malice. This suggests some important distinctions between lying and making untrue claims.
One obvious distinction is that a lie requires that the person believes they are making an untrue claim. Naturally, there is the practical problem of determining whether a person really believes what they are claiming, but this is not relevant to the abstract distinction: if the person believes the claim, then they would not be lying when they make that claim.
It can be argued that a person can lie even when they believe a claim, that what matters is whether the claim is true. The obvious problem is that the accusation of lying is not just a claim the person is wrong; it is also a moral condemnation of wrongdoing. While “lie” could be taken to apply to any untrue claim, there would be a need for a new word to convey not just a statement of error but also one of condemnation. Going back to the test example, it would be odd to say that a wrong answer on a test is thus a lie.
It can also be argued that a person can lie by telling the truth, but by doing so in such a way as to mislead a person into believing something untrue. This does have a certain appeal in that it includes the intent to deceive but differs from the “standard” lie in that the claim is true (or at least believed to be true).
A second obvious distinction is that the person must have malicious intent. This distinguishes untruths of movies, stories and shows from lies. When the actor playing Darth Vader says to Luke “No. I am your father.”, he is saying something untrue, yet it would be unfair to say that the actor is thus a liar. Likewise, the references to dragons, hobbits and elves in the Hobbit are all untrue, yet one should not brand Tolkien a liar for these words.
The obvious reply to this is that there is a category of lies that lack a malicious intent. These lies are often told with good intentions, such as a compliment about a person’s appearance or when parents speak of Santa Claus. As such, there are lies that are not malicious and often called “white lies.” If intent matters, then this sort of lie is much less bad than the malicious lie. They do meet a general definition of “lie” which involves making an untrue claim with the intent to deceive but the deceit is supposed to be benign. Naturally, there are those who would argue that such deceits are still wrong, even with good intentions. The matter is also complicated by the fact that there seem to be untrue claims aimed at deceit that intuitively seem morally acceptable. The classic case is, of course, misleading a person who is trying to murder someone.
In some cases, one person will accuse another of lying because the person disagrees with a claim made by the other person. For example, a person might claim that Trump wants to help average Americans and be accused of lying about this by a person who hates Trump.
In this context, the accusation that the person is lying seems to rest on three points. The first is that the accuser thinks the person does not actually believe their claim and is engaged in an intentional deceit. The accuser also thinks that the claim is not true. The second is that the accuser believes that the accused intends to deceive and expects people to believe them. The third is that the accuser thinks the accused has malicious intent. This might be merely limited to the intent to deceive, but it typically goes beyond this. For example, Trump supporter might be suspected of employing their alleged deceit to encourage cruelty and fascism. Or maybe the person is trolling.
So, to be justified in accusing a person of lying, it needs to be shown that the person does not really believe their claim, that they intend to deceive and that there is malicious intent. Arguing against the claim can show that it is untrue, but this would not be sufficient to show that the person is lying, unless one takes a lie to merely be a claim that is not true. On this view, if someone made a mistake in a math problem and got the wrong answer, they would be a liar. What would be needed would be adequate evidence that the person is insincere in his claim (that is, they believe they are saying the untrue), that they intend to deceive and that there is some malicious intent.
Naturally, effective criticism of a claim does not require showing that the person making the claim is a liar. In fact, the truth or falsity of a claim has no connection to the intent of the person making the claim or what they believe about it. An accusation of lying moves from the issue of whether the claim is true to a moral dispute about the character of the person making the claim. It can, of course, be a useful persuasive device to call someone a liar, but by itself it does nothing to prove or disprove the claim under dispute.