Lying is an important social and moral category. We react negatively to liars and their lies. But what is it to lie? The standard view in philosophy and social science is that a lie is a dishonest assertion. This view goes all the way back to at least the 4th century, when Augustine wrote, “He may say a true thing and yet lie, if he thinks it to be false and utters it for true.” On this view, lying is a purely psychological act: it does not require your assertion to be objectively false, only that you believe it is false.
About two years ago, my son Angelo came across an expression of the standard view of lying. He wondered whether it fit the ordinary concept of lying. (You might be able to imagine the sort of dinnertime conversations that could lead a twelve-year-old to become curious on this point.) In particular, Angelo was interested in whether, on the ordinary view, lying was a purely psychological act. So we conducted some behavioral experiments to find out.