What is a lie? It's not really the opposite of telling the truth, for one can be honestly mistaken in speaking falsehoods. An initial modification would be to say that lying is telling falsehoods on purpose. But do lies actually need to be false? I'm not sure if the concept is clear on this point. I would have thought that actual falsehood is unnecessary: whether a statement is a lie depends solely on the intentions of the speaker. But sometimes people seem to treat the concept differently, and I guess it does sound a little strange to say that a true statement could be a lie.
Consider the following case: Weevil believes the Earth is flat. But, nasty little bugger that he is, he wants Columbus to sail over the edge and fall into the abyss. So when Columbus asks him whether the Earth is flat, Weevil says it isn't. He was intending to deceive, but accidentally ended up telling the truth. Did Weevil lie?
Setting the factive issue aside, intending to tell a falsehood is still insufficient for lying. After all, one might be telling a story or a joke, or engaging in hyperbole or sarcasm. The speaker's higher-order intentions clearly matter here. The speaker must intend to deceive the audience into mistaking what he truly intends, thus leaving them vulnerable to false belief formation. Anyway, that's all pretty straightforward stuff. I'm mainly just curious to hear whether people think lies have to be actually false, or if the intent to deceive suffices.
What if the speaker 'slips' and accidentally says what they believe to be true, when they meant to say something false. Although they acted with intent to deceive, it seems odd to call the slip a 'lie'! So I don't think we should be too subjectivist here. Lying involves more than just deceptive intent; I think the liar must also say something that they genuinely believe is false. If they slip up, then they failed in their attempts to lie. They intended to lie, but ended up speaking honestly by mistake. This seems possible. The question now becomes: how far does this objectivity extend? Is it possible to think you're lying when in fact you're not, just because what you think is false actually happens to be true? Or are actual truth values strictly irrelevant, so that there's nothing problematic about true lies?