It occurs to me that one way for a quasitorial investigation to be assured of clear testimony would be based off of the level 4 perdo mentem guideline diminish a single mental capacity of a target.
A spell that radically diminishes that caster's own ability to lie and be deceptive would be level 5 (base 4 +1 duration diameter). A spell of this sort could be put into a casting tablet, any magus without incompatible arts or some other weird flaw would be able to manage a level 5 casting tablet. At range personal magic resistance isn't an issue.
Now I'm sure that casting a spell could be faked, but witnesses could examine the testifying magus with a spells that don't involve mind reading. A very specific spell that identifies the presence of the truth telling spell could be made at, well at least level 15 (base 5 +1 touch, + 1 diameter), possibly lower if you accept that "detect this particular spell" should be a lower level than "detect any active magic". This would allow pretty good penetration, possibly this spell also could be put a casting table that includes monster amazinly good penetration.
This allows fairly reliable testimony at a lower level than frosty breath of the spoken lie (which would be level 15 for a range personal version). It also allows that magics used to ensure the truth of a testimony are on tablets and thus available for examination by all parties to show that the spells are on the up and up and are not going to reveal more than the witness wants to or leave the witness the mind slave of the person taking the testimony. It allows the person using the spell to provide magically verified testimony without lowering their parma. By being an alternative method to frosty breath of the spoken lie it makes the challenge of creating a magical method to deceive the powers of the investigators more difficult in that the maga or magus who wants to do the deception doesn't know what method they'll have to overcome in order to lie convincingly.
It isn't hard to imagine that every tribunal has a pair of casting tablets of this description copied by some Gurnicus apprentice many years ago. The cost of creating this is minimal.
Does this seem reasonable? What are the best ways to fool it? heck what are the best ways to fool frosty breath and or ear of truth (the target hearing InMe lie detector spell from true lineages)?
One effective way to mess with truth detecting magics is to use muto mentem spells on oneself so that what you want to say lines up with what you actually believe. Switching your memory for duration Moon will allow you to testify and then later recover the truth of the event.
The weakness of this is that you have an active mentem effect on you that can be detected. But it is illegal to scry on another member of the order so that might well be a weakness that you can live with.
A counter that the investigators could use is casting a perdo vim "unraveling the fabric of mentem" spell, this would restore your actual memories just prior to testifying. A range personal version of unraveling the fabric of mentem could be another casting tablet that one might expect a tribunal have. This would once again allow a witness to demonstrate the veracity of their report by casting it upon themselves prior to giving testimony without the worries associated with having some other person throw mentem spells at your mind.
Going further down the path of how could a person beat this. IIRC the order of suleman has effects that can change a memory and leave the altered memory after the magic ends. In other words, there would be no magic to detect or dispel. While spell traces or quasitorial sensory magic spell mastery might be able to figure this out, neither of these things is legal to apply to an unwilling magus.
The best way to defeat Hermetic lie detection would involve diabolism, since demonic lies can't be detected by Hermetic magic. Not sure exactly what method would be the best compromise between "less disruptive to the diabolist personally to cast" (as in, how much would you let yourself get possessed by a demon) and "more effective."
You can also do some serious Muto Mentem and physically pull your memories out of your mind, leaving them in solid form back at your sanctum (or burying them in a box in the woods), so that you're not lying. Reintegration might be problematic, and lots of warping. Would prevent even intrusive Intellego Mentem and might be a good MacGuffin for an adventure, though.
Barring that, a better way to defeat the tablets than using an active magic is to use a Rego Mentem along with Art of Memory to place the offending memories somewhere in you mind that, unless you have your full faculties, you cannot reach.
If you're really, really willing to risk losing memories long term, you can cast a temporary Creo Mentem on yourself for even greater mental acuity and jam something up there that you can't get access to unless you cast a CrMe spell on yourself again; this would also work against Frosty Breath.
If you're willing to warp yourself significantly, you could do a number of ReMe-based ritual spells (some likely with co-requisites) to turn your entire mind into a warded puzzle box such that it does not open unless you want it to. Combining this with magics from one or more Mysteries (Criamon labyrinths, dream magic, and planetary magic immediately come to mind) and you might be able to protect the contents of your mind from being released except under specific preplanned conditions that you believe only exist when you are free of others' influence or coercion.
Here's a simple solution, use perdo mentem to destroy problematic memories. There is nothing to see but the spell traces.
You could make it better by first doing a creo mentem spell to create false memories then using perdo mentem to destroy all of the problematic memories (obviously including the magical manipulation of your mind) then the duration of the creo mentem spell ends. You are left with the memory of thinking about the now missing synthetic memories and no recollection of the true events. Once again you've only got spell traces. I don't think that quasitorial sensory magic mastery would apply to it because your remaining memories are not magically altered (it might be able to suss out the fact that some memories are missing but intellego mentem specifically to see a target's complete memories with magical sense targets and the correct spell mastery isn't at all common).
A Muto Mentem spell with the faerie duration of until can not be dispelled by normal means (p.92). "I change my memories until the tribunal has resolved the issue in my favor", the investigators can detect that your mind has a muto mentem effect on it but thy can't dispel it.
You could cast a big unraveling the fabric of mentem on yourself and still be good.
I agree, the fact that duration until requires a ritual and is a +4 magnitude parameter means that botches are are a threat. This makes things more dramatic.
Actually, it is impossible for me to imagine. No one ever thought of this until October 2015, nearly eight hundred years after the cannon start date.
:mrgreen:
Being smarmy aside, it is reasonable and easy for me to imagine that the Q's started doing this sometime in the 1240's (where my saga is currently) and it is a new procedure that is not yet common or widespread.
Don't casting tablets have a quirk that preserves the sigil of the author? If a quaesitor has access to several casting tablets of the spell with different authors, wouldn't it be difficult for a magus to fake the correct sigil if he's not aware of which version of the tablet he's been given?
I agree. This is a cool idea. Also difficult for somebody to recover the missing memories from your mind (as you have not changed or destroyed them, just put them somewhere else). Although where you have put the missing memories might be recoverable.
Yeah, I think that this is the best option. Of course, relies upon you not wanting to recover the memories yourself at some point.
Once the PCs start down this path, there is heaps of opportunity for paranoia. The PCs are no longer sure quite what they have done, or whether or not they are responsible for the problems that they themselves are investigating.
I once played in a great Vampire campaign along these lines where my character had a memory that had been turned to Swiss Cheese in a similar way by (his Sire's / Grand Sire's) Dominate powers.
I hadn't thought of that, if the sigil is something that can be observed by others that makes it necessary that someone fake casting figure out what the sigil is and then fake it.
The problem with destroying the memories is that the character/NPC might wonder why they are missing a day of memory. Many a good book/show has had this set up. The recent Heroes Reborn comes to mind as well as Richard K. Morgan's Altered Carbon. Again, more of a MacGuffin for players as a senior mage asks them to find out who erased a day or so of his memory.
I think a much more satisfying story is the PCs realising that a day (or more) of their own memories are missing or inconsistent. And then trying to find what is missing and who did it. And becoming paranoid that they did it to themselves For A Good Reason.