MuVi and magic items are pretty clear cut. The MuVi effects only work on effects in the item (unless you have Consummate Talisman), but that is a special issue with MuVi and does not apply to ReVi. In particular, I'm looking at Maintaining the Demanding Spell and Opening the Intangible Tunnel or versions of them.
I'm also looking at Talismans. With non-Talismans items the item is clearly separate from the user - no problem there. But with Talismans there are some rules that blur these lines. The Talisman considers itself and the user (here assumed to be the one to whom the Talisman is bound) to be the same when touching as far as affecting each other with spells (R: Personal effects apply to the user). The user considers the Talisman to be part of himself (including applying for R: Touch).
So, now my questions:
If a magus puts Opening the Intangible Tunnel in his Talisman and activates it, can the magus cast his own spells through the tunnel as long as he is in contact with the Talisman? It seems like "yes," but it's murky since the Talisman isn't the magus himself.
The magus puts a version of Maintaining the Demanding Spell in his Talisman. If he only wants it to work when he is holding his talisman, can he use the normal Maintaining the Demanding Spell guideline or must he use the divide by 2 guideline? It seems like "yes," but it's murky again since the Talisman isn't the magus himself.
Overinterpretation. Just because a Talisman can affect the bonded user at R: Personal, we do not automatically get that they are considered to be the same entity. Indeed that would have been a more concise way of communicating that the R: Personal trick worked, and how the Talisman extends the 'touch' of the bonded user. If anything, the formulation (that these 2 effects are explicitly enabled) would indicate (to me anyway) that the Talisman and bonded wielder are not to be considered a single entity.
I think I made a similar argument with Erik Tyrrell here.
Trivially. Anyone can use (Hermetic) magic through a given Intangible Tunnel, assuming (s)he is aware of it (ArM5, p. 162, perhaps more clear from Projects, p. 79).
Now, one could ask if you can automatically sense an Intangible Tunnel cast by your own Talisman, presumably triggered by your will. I'd say yes, but if that is not the case, investing an effect to make it so would be fairly trivial I think.
Again, as far as I can tell, the Talisman is not the bonded user, even though it gets certain perks. I'd require use of the "divide by 2" guideline (or the "specific type of spell only" guideline, HoH: S, box, p. 129).
Infact, I'm reasonably sure I convinced Erik he'd need to do just that.
As long as a caster can sense a tunnel he can use it to cast spells through, be that tunnel created by his talisman, another magus or an arbitrary magic item.
If the item creating the tunnel is his talisman and he holds it, he is touching the local end of that tunnel. IMO this should count as sensing it. But a base 5 InVi spell detecting it can easily be cast before creating the tunnel, resolving that problem anyway, even if another magus or a more normal enchanted item created it.
This leads to interesting situations, if a magus holding an enchanted item which just created a tunnel is counterattacked by his target, and then drops the enchanted item.
Ah, the HP text differs from the ArM5 text by adding that note about either end, though that still doesn't answer the sensing question as you both noted.
Also, something I forgot note above: I had also looked at Consummate Talisman, noting the odd R: Personal instead of R: Touch for MuVi. R: Touch is required for your own spells, while R: Voice is required for someone else's spells. Assuming R: Personal is a slight bonus on R: Touch, Consummate Talisman is using the guideline for casting a spell yourself, not for someone else casting a spell. This is a Virtue from a Mystery, which could explain it. However, I don't see why someone with Consummate Talisman would have a Talisman that is drastically worse at ReVi on his own spells than it is at MuVi considering that the ReVi is much easier, not even requiring Consummate Talisman. This had highlighted the conundrum for me.
In Legends of Hermes, on p65, is an enchantment for a touch-range version of 'maintaining the demanding spell' - Range: Touch, Duration: Diameter, Target: Indivual.
The following errata (see errata page) gets added:
"This effect was invested in Fortunata's Talisman, and takes advantage of a Talisman's closer connection to the maga who created it. It cannot be used by any other magus, although laboratory investigation does reveal its existence and nature."
This implies that talismans are indeed 'the magus' for purposes of ReVi spells.
OK, cool. As you could tell from my OP, I couldn't follow a clear line of logic to rule one way or the other for sure. Either had a certain amount of validity, but nothing was definite. Having a canon interpretation is nice. Thanks, Kid Gloves!!!