Just a question...
Is it possible to detect with the virtue premonition when someone is about to lie ?
I would say no but....
Premonition warns about dangers and problems ahead so it may warn you of a danger if you decide to act on the basis of a Lie told to you but if that Lie will not cause you a problem or endanger you then premonition will not give you a premonition , even if it does warn you it will not automatlcally warn you that someone lied to you at the basic level all you will get in an instinctive warning that something bad will happen soon while a good roll may tell you that if you go throught the door you will be stabbed (and if the man you are talking to hust told you it was safe you would conclude he lied or did not know)
Premonitions is a tricky one. Bear in mind that it can be rolled by Storyguide or player against an Ease Factor. It isn't Guile and it isn't Intrigue, so I'd rule against making it a substitute for those abilities and allowing a roll to determine whether someone's telling the truth or not.
If it's an NPC and as a SG I know he'll lie, I might roll against Premonitions early and see whether the character gets any kind of hint; "the man you are looking for will lie to you". But that's different to detecting a lie as it is spoken, after all, how do you determine which is the lie and which isn't? It at least puts you on guard against deception.
No.
If the lie causes you danger than you can roll. Not because of the lie but the danger itself.
Ok.
I get the point.
A second question about this virtue:
Does it need to penetrate if the interlocutor has a magic (infernal/faeric) resistance ?
I don't think so, if it's related to the danger, and not the guy you have in front of you, but I'm not sure. What do you think ?
And a third question:
If it determines the danger linked to the lie, it should warn against half-truth as well ?
premonition is "premonition",
It's the abilety to have a foresight on the future (which will be bad for you).
For me: lies are not endangering. If the guy has decided to hurt you, premontion could (or not) have already "ping-ed" you. But the lie, in itself wont ping your special ability.
And premontion are... dreams, sensations, ideas, impressions... not analyze of danger.
I suggest a gamewise solution. The character has a lot of points in his ability which he can use rarely. Thus I would favor the character saying there is no need to penetrate. But only within the range of the ability. Lie detection is not part of this ability. That's Folk Ken. The ability warns him only before the character want to act somehow. Sometimes passivity may be dangerous, too.
It does NOT warn against a lie OR a halftruth! It may warn against danger presented by beleiving those.
AFAIK, penetration has nothing to do with it in any way.