The Emperor doesn't have a son Fëanáro's age but if I'd been found hiding him from his father and he was sitting on my lap learning unauthorized lessons that would be another problem from the Emperor's perspective. Anyway, he would assume that if he asked me if I was trying to kill him and I was in fact trying to kill him I'd still say 'no'.

But obviously, knowing that, you should just decide to be the sort of person who would answer the Emperor truthfully.

...but assassins wouldn't do that, so it wouldn't matter if I did.

...everyone has to do that. It's the most important thing for a society to get right! Even if they're an assassin, they should have that decency.

Um, more important than not assassinating people?

That's also important, but seems like it'd come up much less. You could give your word to speak the truth? I mean, if your life depends on it -

If he wouldn't believe me when I said I wasn't an assassin he certainly wouldn't believe me if I said I wasn't a liar.

No one would swear falsely just to get out of execution!

...um, anybody would swear falsely to get out of execution. At home.

But that's a fate much worse than death.

No... it's not...? Um, what are you talking about?

He's incredulous. Have you ever sworn falsely?

Do you just mean lying in general or something more elaborate?

I mean, given your word, intending that it bind you or being interpreted as intending that, and then not following through on the sworn course?

I don't know if I've ever done the exact thing you described per se because this isn't something people ask of others on a routine basis at home, but I wouldn't expect anything interesting to happen if I did...

Well, you can't break it. You'll suffer horribly and feel nothing at all, no pleasure and no desires, save for a constant longing to do as you swore.

I can imagine that you would have, yes. Huh. Anyhow, that's what happens to us. No one gives their word except in desperate straits, but in those it can achieve a great deal. For example, your Emperor wouldn't need to execute suspected assassins if they could swear they weren't.

I suppose, unless he thought they were choosing their words really carefully and were conspiring with assassins, or were spies instead, or something like that.

In that situation, I would simply give my word that I would not, in the next hour, tell any lies. Up to him to come up with appropriate questions.

Well, he'd probably want you to swear not to tell his professional interrogators any lies; and he'd have to know that you were a whatever your species is called and that this property of the species is reliable; but yeah, I guess that would work, or at least it'd work if there weren't an established policy on how to deal with palatial intruders.

That policy being to kill them? That seems unwise. If you had been an assassin how would they learn who'd sent you?

I didn't say they'd kill me right away.

You're not implying they'd harm you to get you to stop shielding your private thoughts?

Sure they would. We're talking about people who are hypothetically planning to kill me.