And what is a liar?

And what is a liar?
My son asked me
How do you tell
When the chips are down?

Who blinks, I said
And looks away
And fidgets and thinks
Of another day.

Still puzzled he said
But, how do you tell?
The long stories and all the facts
Laid out in rows and logical racks?

That’s more subtle, I said
Some believe their lies
And if lies are believed then where is the lie?
And where is the truth, if truth you want?

Still puzzled he looked
And so should remain
For truth and lies are subtle constructs
And outside the ken of our mortal domain.