Is it a lie if you did not intend to deceive anyone? If you said something you believed to be true, but was not, then your intent was not to deceive, and I would not call you a liar, merely ignorant. If, however, you start from the definition of absolute truth, then saying something that is not true is a lie, whether you knew it or not. The trouble with that second definition, though it is more useful in picking truth from untruth, is that it muddies the definition between who intends to deceive you (and cannot, therefore, be trusted) and who is merely ignorant (who may be trusted to be honest, but may need some fact-checking).
Mokalus of Borg
PS - A polygraph only aims to detect the intent to deceive.
PPS - If it could do more, it would be a very strange device.