plot device - How does the magic in "Liar Liar" work?

In Liar Liar, Jim Carrey gains the superpower of not being able to lie for 24 hours. Wikipedia defines lying as

... a statement used intentionally for the purpose of deception. The practice of communicating lies is called lying, and a person who communicates a lie may be termed a liar.

Does this mean he just wasn't able to say anything deceptive, or does it mean he wasn't able to say anything that was false? I always thought it was the former, but there is one scene in the movie where he says...

I'm a bad father

...then looks shocked that he was able to say it on the day he wasn't able to lie, indicating that, according to the movie's logic, he cannot utter false statements. In short, my questions are, in Liar Liar, can Jim Carrey say a statement if:

1. It is true but he genuinely believes it to be false?



2. It is false but he genuinely believes it to be true?


3. It may be true or false but he has no idea either way?

Answer

In the original script, we see that Fletcher's incapacity is that he can't say something that he knows to be untrue. This includes not being able to hand a (previously written) statement that he knows is untrue to the judge in the divorce case.

He is, however able to be somewhat deceptive, as long as he doesn't actually lie. On several occasions he does say things that are strictly true, but ends up giving a misleading impression.

JUDGE STEVENS: Strong corroborating evidence?

FLETCHER: We have evidence that you are not going to-believe.

[Despite herself, Dana is beginning to look worried.]

JUDGE STEVENS: You're pretty confident how this trial is going to come out, eh, Mr. Reid?

FLETCHER (hopeless): "Confident" is too weak a word, Your Honor. I am certain what will happen if I take this puppy to trial. The verdict will be a stunning, humiliating defeat that will cut a spectacularly promising legal career off at the knees.

[Fletcher is referring to himself, of course, but Dana thinks he's speaking about her. She buckles.]

Note that despite the fact that she's clearly misunderstood what he meant, Fletcher feels no compulsion to correct her.

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Fletcher is also able to say things that are objectively false (untrue) as long as he believes them to be true. He states that the distance between Los Angeles and Boston is "3000 miles", however a quick look at the map reveals that it's only 2800 miles by road or less than 2600 miles as the crow flies.

FLETCHER: You can't go. It's not fair. Taking Max three thousand miles away is not fair.