Second Sight lets you see invisible things pretty easilly, not needing to penetrate resistance and such. To see naturally invisible things, such as a spiit, is a low ease factor of 9.
My question is, if the spirit is inside of something, can you still "see" it? For example, I am a ghost animating a corpse. Could you still see the ghost, or would your view be blocked by the corpse it is encapsulated within? What is the appearance of the spirit is identicle to the corpse?
Can you see a guy encassed in armour? There you go 
I would not allow it. Has worked well so far IMS and I have no complains. In fact, second sight is the most common virtue IMS, I think.
Cheers,
Xavi
You would almost certainly see that there is something IN the corpse i would say. Might take a bit of effort(or success) to see that it is a ghost though.
How can you when you cannot see inside the corpse?
Will a ghost be able to be inside a corpse in such a way that it doesnt show on the outside or make the corpse look different than normal in any way?
I would say totally NOT!
Hmm, therin lies the difference. I would say totally yes. A ghost wears a body like a hand wears a glove. AND, if the corpse originally belonged to said ghost in the first place, then it would be a perfect fit. Now, I am talking about a perfectly preserved corpse. Not a dead body. A corpse made with ritual Creo magic, in perfect condition.
I am interested in hearing a diversity of points of view. I already made the ruling for a specific scenario in my game, but it may influence future decisions.
I have recently ruled that if a living person is possessed by a spirit a good second sight roll can see the possessing spirit as it is not quite a perfect match for the body. I would on the same basis allow a spirit possessing a corpse to be seen. If the body was protected by a Parma magica other than that of the spirit I would require the parma magica to be penetrated to see the possessing spirit.
I think if anything should be able to detect a possession or the like it is second sight. Physical concealment to such a minor degree as the body and accoutrements and the like is unimportant in this circumstance to me.
If a ghost is riding someone, whether they are wearing armor or not, I'd say someone with SS should get a roll to see either the spirit superimposed on the physical body. That or something similar that reveals the spirit's presence.
The same with any kind of Intellego Vim effect that can detect a spirit.
Would then, in your opinion, sense holiness and unholiness detect demonic possessions??
I would think that might depend on the SG.
Looking at the write up in the Core Book, the virtue seems to allow someone to sense the presence, not the particulars. So you might sense that the person is Unholy. But that could mean the person is also a diabolist, or a demon in disguse, or some such. Some SGs or Troupes might rule it allows more than that though.
I however have not read all of RoP Infernal, so there may be more there.
I think is a YMMV ands IMS thing. IMS you might detect something that makes you uncomfortable about the guy, but unless the demon is moving in full sight (even if invisible or non-corporeal) you can't see it. There are plenty of stories where the demon rides a person and until he reveals himself he cannot be seen, even if the guy can be detected to "have something evil in him".
Xavi
Absolutely. It is a sense, not a sight.
Exactly.
And don't forget - nothing says that two "spirits" have to work the same way. One possession might be perceivable, another not, or with different difficulty numbers. It's a wild mythic world out there - no reason to think it can be predicted with a sheet of graph-paper and a straight edge. 