Truth, lie and sin

I was replying to some posts at Vox Day and got into a hole so I thought I'd start afresh and think through what is truth, and lies and what is reality. (Not too different from my attempt to write about language and consciousness.) (Started this 8PM Jul 8 but I've extenstively updated since then...)

Truth is actual description of what is now or has been.

Lie is anything less than 100% fidelity to truth.

Language is the only way to describe truth. Yet because language transcends reality, truth can easily be turned into a lie by removing/changing/adding 1% of/to the truth. So as we forget stuff, do we lie on purpose or lie "accidentally" as time passes? Especially as we embellish the past either positively for our good guys (including our own selves, of course) or negatively for our bad guys (i.e., enemies).

With the above definition, is it wrong to lie? Is lying sin, even if we temporary forget a minor detail which is only 1% wrong? Or does it become sin when it's 50% wrong? 75% (or more)?

Or how about writing fiction? Or even parables (of which Jesus loved to use)? It isn't real so by my definition above it is a lie but is fiction a sin? I don't think so.

No human can avoid lying with the above definitions. (Dictionaries aren't so exacting, by the way.) Only God can be spoken of: "God is not a man, that he should lie" (Num 24:19). (Note: Metaphors and parables don't seem to count as lying, if this verse is to be taken seriously -- so my definition is waaay too strict in the first place. (grin))

Which is why I believe God did not put "you shall not lie" in the 9th Commandment. You can read it for yourself:

You shall not give false testimony against your neighbor. (Exo 20:16, Deu 5:20)

Does this mean we can lie (in general) with impunity? Well, here are some laws from Lev 19:

Do not steal.
Do not lie.
Do not deceive one another. Lev 19:11

Which seems pretty clear. Even Jesus doesn't mince words when it comes to lying:

You belong to your father, the devil, and you want to carry out your father's desire. He was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies. John 8:44

And lying can even result in capital punishment:

"You have not lied to men but to God." When Ananias heard this, he fell down and died. See Act 5:1-11

Just kidding: what really happened was that Ananias and Sapphira promised to God one thing and acted another. They broke their promise and their lies only confirmed it. So it's hard to argue that their lying caused their deaths.

However, there are some lying which are either condoned or just not condemned, like the story of Abraham lying to escape death (cf Gen 12:10-20 and Gen 20:1-17) or, like father like son, Isaac lying (Gen 26:1-11) or, the grandsons of Abraham story of Jacob (Israel) taking Esau's blessings (Gen 27:1-40). (What a way to start the Jewish nation, huh?)

The classic, for me, is with the story of a Gentile prostitute:
Rahab took in Israelite spies and hid them and then lied to those hunting for the spies (cf Joshua 2:1-24). She, in turn, not only saved her own life but also her family's lives (Joshua 6:22-23, 25). And, she gets named with the other saints of faith in Hebrews 11:31. Also, her action of hiding the spies was commended as righteous in James 3:11 (even though she had to lie to protect them).
So what is the principle of truth and lying? 9th Commandment makes clear that false witness against others is wrong. What Satan did to deceive Eve (and Adam) was wrong (but I guess he did break the 9th, afterall, with "false witnessing," in this case, against God -- see Gen 3:1-15). Any other obviously wrong forms of lies (other than covering up other sins like what Ananias did)?