I am actually trying to look at this from a philosophical perspective, David.
Let's see what some dictionaries say a "liar" is...
Most just say "One who tells lies," but we already see some caveats coming out:
n. One who lies; a person who knowingly utters falsehood; one who deceives by false report or representation.
Meaning, someone who is only saying something that they know to be untrue.
So a person who is mistaken is not a liar, right?
Now, what is a lie?
n. A false statement deliberately presented as being true; a falsehood.
n. Something meant to deceive or give a wrong impression.
v. To give false information intentionally.
v. To convey a false image or impression.
(American Heritage Dictionary)
n. A falsehood uttered or acted for the purpose of deception; an intentional violation of truth; an untruth spoken with the intention to deceive.intransitive v. To utter falsehood with an intention to deceive; to say or do that which is intended to deceive another, when he a right to know the truth, or when morality requires a just representation.
(Collaborative International English Dictionary)
n. A false statement made with the purpose of deceiving; an intentional untruth; a falsehood; the utterance by speech or act of that which is false, with intent to mislead or delude.
n. That which is intended or serves to deceive or mislead; anything designed or adapted to produce false conclusions or expectations: as, this epitaph is a lie.
Indeed, it seems to be quite common place to suggest thatmy definition of what a lie is is entirely valid.
Indeed, it seems to be the norm,
and certainly to be reflective of what any very serious usage of the word would mean.