So, I'm reading through the Hedge Magic book, and I come across the Second Sight integration rules - it allows you to cast Intelligo spells that don't require penetration. OK, sounds good. But what about the OTHER ability of Second Sight - the ability to reliably (albeit with difficulty) detect demons? In the saga I'm in, that power is much more useful than the no-penetration integration. Is that ability implied in the integration, is it excluded, or is it considered a separate integration ability?
Thoughts:
I'd like it to be implicitly integrated, but that would imply that a demon's ability to lie is related to spell penetration. Which I suppose it could be: the spell isn't actually affecting the target (ie, no penetration), so therefore there is no way to lie to it. But that's a quirky bit of reasoning, IMO.
If it's specifically being excluded, then that implies a flaw in hermetic theory that prevents this integration from occurring. But it's not a flaw in Magic itself, as Second Sight itself can detect demons. And that line of reasoning sounds odd to me.
If it's a separate integration ability, it really should have been mentioned: "Intelligo Vim (general): Detect demons whose magic might is equal to the Magnitude of the spell +10" (Or something like that.)
Or, it could be the author implying "troupe's option". Which is a fine enough answer, although I'd prefer something a bit more explicit.
Can you quote where you got the idea that Second Sight works against demons?
I would direct you to RoP:I p33 which kinda contradicts your affirmation. "If this Ability derives from non-Divine sources, then it may not pierce illusions created by demons at all;"
Hm... I was under the impression it was Difficulty 9 + (demon's infernal might/5), whereas the Divine version was a straight-up Difficulty 9. I'll check my books when I get back home tonight. (Or I could be thinking of a different Ability...)
Option 5 is that the author didn't think of it at the time.
However, being able to detect demons reliably is a separate thing from needing to penetrate with magical senses. With vanilla Hermetic magic, if your magic sense has sufficient Penetration to Penetrate a demon's Magic Resistance then you still can't reliably detect him, due to the Limit of the Infernal. Whereas, under similar circumstances, you can detect a faerie just fine, as long as you can Penetrate its Magic Resistance. So, just removing the requirement to Penetrate from magical senses doesn't also imply that you can reliably detect demons. It's a separate thing.
On the other hand, "being able to detect demons" sounds like a fine (albeit different) research / integration project for which Second Sight could well be a source of insight. Whether it is actually possible or not (perhaps your character is just wasting his time) is a matter for your troupe, as ever. There are lots of other things that could also be used as sources of insight for a project to be "able to detect demons", such as demons themselves. I'm sure that plenty of demons would be interested in tempting a magus to summon and study demons (especially if the demons believed that the project was not actually achievable).
The way I'm reading it, Divine has Difficulty 6+(Might/5) while other cannot at all. I also have a vague memory being completely undetectable when lying dormant inside a victim.
OK, I'm back at home. Nope, looks like Turgdual is correct - According to RoP:I, Magic-aligned Second Sight can't detect demons. I was misremembering the "how to detect a spirit in general for any version of Second Sight" (difficulty 9) against the "How to Detect a Demon" (Difficulty 6+ Might/5, but only for Divine: any other version automatically fails.)