People are lying when they make false statements deliberately with the intention to deceive. I guess to know if someone is lying we need: - to know the facts

People are lying when they make false statements deliberately with the intention to deceive. I guess to know if someone is lying we need: - to know the facts - if the person knows the facts - and the intentions of the person all the rest is just guesswork, woodoo. (and yes, many times we will not know if someone is lying or not. But listening to what a person says and confirming it from independent sources could help a lot in the third of the discovery)