Are you saying it is impossible to ascertain the intent of the speaker? No, not at all. Just that for something to be a lie it needs 1. to be not true, and 2.

Are you saying it is impossible to ascertain the intent of the speaker? No, not at all. Just that for something to be a lie it needs 1. to be not true, and 2. for the person uttering it to know that it's not true. Hopefully that's entirely uncontroversial. Yes, how to find out what people know, desire, plan, intend etc is another question entirely. Another thing - I don't think you can always neatly divide people's utterances into something they know/believe vs something they don't. e.g. believing in god or not - some have varying levels of belief, depends on mood, some aren't sure what they believe etc, it's often not a simple, unchanging binary 'on or off' situation.