I've been thinking, how far can you push restricting the use of a magic item? An example to illustrate my point:
Imagine a book containing a summa on the Parma Magica. To protect it from outsiders, it's enchanted. Normally, the text is missing; only members of a specific group can make the text appear. Would any of these groups be possible? I am ignoring the fact that some of these might violate the "no scrying on other magi" rule.
Idea 1: Those with an active Parma Magica. Now, I imagine this would be the easiest to detect; it's a magical effect that I assume Intellego Vim could detect.
Idea 2: Those whose Gift has opened to the Hermatic Arts. This sounds harder to detect, but at first blush I'm not sure why (intuition, I guess). I imagine Intellego Vim would be it once again.
Idea 3: Those who have recited the Oath of Hermes. Off hand, Intellego Mentem might be able to check if the holder remembers doing so, but can it?
Idea 4: Those who have never violated the Oath of Hermes. Now, I'm fairly sure this is impossible, but let's be daring. In the interest of clarity, it could be Intellego Mentem on the holder's mind to see if they remember ever breaking the Oath.
Idea 5: Those who have recited the Oath of Hermes in the book's presence. InIm/InMe could detect when it is spoken, but can the book really tell? As a side point, could the book remember whose done it or would they have to do it every time?
Ideas 1 & 2 seem pretty straightforward and effective to me. I would start with the difficulty for detecting the Gift and raise it by a magnitude, to detect if that Gift had been opened and how. Extrapolated from, for example, InCo and the Physician's Eye.
Ideas 3 & 4 aren't detecting what a person has done, they're detecting the memory of doing or not doing something. This is pretty basic stuff for an item to do, but it is so easily fooled by Creo or Perdo Mentem magic that I can't believe House Guernicus would consider such an enchantment to be a qualifying deterrent. Someone who acquired the book and studied it could learn how it's enchantments worked, and then destroy their own memory of violating the a Code (or transform the memory into a pearl or something), or create the memory of reciting the Oath even if they never have.
Idea 5 again seems a pretty straight forward InMe effect, detecting the surface thoughts that occur when a person speaks.
Whatever additional enchantments are on the book, they'd be triggered by these Intellego effects. This is very common and there are many examples of items in canon which have similar triggering Intellego effects. This is a very expensive way to protect a book, I'll note, since the book has to be opened for enchantment and then enchanted with at least two effects, so we are spending vis (the lesser cost) and multiple seasons (the greater cost). Doesn't mean it can't be done, or that such books might not even be standard in your saga. It's just expensive. But the Order has been around for centuries and a book like this could have a very long lifespan, so they could slowly accumulate, probably in large and old covenants, like Domus Magna.
You do not really need specific InIm or InMe effects and linked triggers for this.
An empty book might be enchanted - as an invested item or lesser enchantment - with a D: Sun CrIm effect (twice per day) to show its text. Reciting the Oath of Hermes might be part of its complex triggering action (ArM5 p.98). Investigating the enchantment of the book (ArM5 p.100) to find out effect and triggering action is typically beyond the capabilities of hedgies lusting for secrets, or of curious apprentices: but an Hermetic magus needing to discover wisdom of his age-old sodales might succeed with little work.
I really like the idea of a Parma Magica summa that requires the recital if the Oath of Hermes to open it. An incredibly long and complex 'Key word' incantation.
I'm envisioning a simple PeIm that makes the text of the book invisible, but with 0 penetration. Anyone with a Parma who handles the book... poof, the PeIm effect gets Parma'ed!
Unfortunately, any form of MR would do the same thing (as would PeVi spells, or comparable magic-suppressing Hedge Magic). Which kinda sucks, because it's such an elegant solution...
ummm "ymmv"?
Items that do anything with certamen are not part of the RAW, so far as I know...
I'd probably follow the "Yes, but... " principle: "Yes, but it will take some extra research (possibly even a Minor Breakthrough) to figure out how..."
Well, a big enough PeVi could just dispel the PeIm-enchantment entirely, leaving the text mundanely-visible forever. But PeVi can suppress an item's ongoing magic without dispelling the enchantment, so the item's effect will return once the PeVi expires (or the Parma just walks away... ) .
Or just dispense with the ink: Cast a spell on a parchment with Target: Part, so that the spell only affects the part of the parchment in the shape of the letters that would normally be written. Then, an InVi Vision spell would detect the traces of magic only on the part of the parchment that had been affected by the original spell. Sustaining the InVi would allow reading the shapes.
Of course, the original spell has a very fancy effect. But a magic item in the shape of a stylus that continually or repeatedly casts (Touch, Part, Mom) on parchment that it touches can have a much simpler effect, since the magic is no longer responsible for the calligraphy.
Variants of this can cast The Hermetic Mark of Cain on someone; some Tribunals might brand magi guilty of Hermetic crimes with symbols that only be seen by other magi.
One problem with (or feature of) all this is that the spell traces fade with time. As more time passes (and as the initial marking spell has a lower level of effect), higher level InVi is needed to see the markings.
Make it with something like Duration Aura and that would also help with security as the "writing" would when it left the covenant. I'm not remembering how hard Duration Aura is, or where I read of it...
The duration won't matter here comma because once the spell is cast comma even if it is a momentary spell duration, there will be magical traces that an Intel Lego themed can catch.
And Google is not doing completely well with getting what I say.
Please remember that the Followers of Pendule are not the only ones to teach Perpetuity.
Indeed, it is also listed for the Shadow-Masters, HoH: MC, p. 82-83.
