A lie is a statement:
- designed to make the reader/listener believe something that is false
- where either the author knows is not true
- or where the author is not expert enough to know whether it is true or not, but is claiming otherwise.
Notice that this means that a sentence that is literally true can still be a lie. There is a reason that the legalistic phrase “false and misleading” is used; those are not synonymous. (E.g., Parent: “Were you out past curfew?” Teen: “I came home just before midnight, like you said.” Reality: the kid then sneaked back out at 12:30. E.g., “Smokeless tobacco is not a safe alternative to smoking.”)
Indeed, it is usually the case that lies in the form of literally true statements are ethically worse than literally false statements. In the latter case, someone might be genuinely ignorant. In the former case, the careful crafting needed to lie with literally true sentences strongly indicates that the author knows the truth and is going to great lengths to communicate the lie; thus, there is not mere ignorance, but malice.
When there is genuine ignorance, a lie occurs if the author claims to be expert in spite of actually being ignorant of the facts or incapable of understanding the science. Obviously that is a little fuzzy around the edges, since in normal discourse, people often make claims that turn out to be wrong even though they have some expertise. But in clear cases, no such “honest mistake” defense is possible. If someone claiming expertise on a subject makes definitive declarations in highly-non-casual communication — e.g., an interview with the press or a crafted written statement — and those declarations tend to make readers believe something that is clearly false, then they are lies. They are lies either in the sense of the author knowing the communicated message was false or in the sense of the author claiming to be sufficiently expert to make the claim.