Ok, I tried searching the forum, I red the rules twice and could not find it :
Is there anything in the RAW preventing someone from casting a spell for wich he doesn't have the virtues (for example faerie magic) using a casting tablet ?
(I had a heated argument about this on the french forum and would like a definitive answer)
Also, if the author stop by could he tell us his intent about this ?
Nothing definitive as far as I can tell, but the Ward Against Woodland Spirits Casting Tablet in Legends of Hermes p. 27 can be used to integrate the True Understanding of the Realms virtue, but it is castable without. So you could conclude that the Casting Tablet contains just enough of the virtue to make the spell castable.
ArM5 isn't a game which, when introducing a new possibility, attaches a long list about what that possibility does not do. The function of casting tablets is summarized completely as:
(underscores mine as usual). There is nothing said about magi who absolutely cannot invent or learn a spell in the lab to cast it - e. g. due to Flaws (like Rigid Magic) or lack of Virtues (like Faerie Magic). So by RAW casting tablets do not compensate for these.
A non-standard spell resulting from an experiment, however, can be written up as a lab text, distributed and learned. If somebody masters it, she can write it up as a casting tablet as well, to be cast by those who could learn it through laboratory research. The LoH p.27 casting tablet should provide such a spell.
Cheers
EDIT: Added a needed precisation in italics. Thanks to Jonathan.Link for noticing.
FWIW, Rigid Magic doesn't prevent a magus from learning a ritual spell, only from using vis during spell casting
If the magus who possessed Rigid Magic tried to perform a ritual from a Casting Tablet, he would be unable to do so, because the ritual doesn't allow him to use vis when casting spells. A magus who has Rigid Magic, who knows a ritual spell and has it mastered, could create a Casting Tablet for that ritual.
You know, it might be useful to have the address of that forum.
I also believe that it should not be argued whether it's right or wrong, but rather what are the issues behind it. RAW should only be the default, uninformed decision of the Troupe.
Background around the issue :
Gwydion Ex Merinita has Rigid Magic, he creates a ritual spell, master it and write a casting tablet.
He then give that casting tablet to Octavius Ex Bonisagus (who as strong faerie blood) who cast the spell for him.
So would you have allowed it ?
Specifically for Faerie magic : the virtue does not prevent someone who doesn't have it from casting a spell that need it, it prevents him from learning it. I know it's a slight difference but it's clearly stated in the core rulebook (but i see your point).
further more, as all hermetic virtues were invented by laboratory research it could be argued that it is implied here that you can use the casting tablet.
But you make a distinction that doesn't exist in the rules between non-standard spells by experiment and non-standrad spells using virtues. In addition there are proof on the rules (legacy spells, the spell conatined in the tome of binro...) that you don't even need a casting tablet for slightly non-standard spell.
Lastly the spell from LoH "subsuming the apparent dominion" is a spell that require specific actions for the magus to obtain the guideline (reading an unpublished book by Conciatta) so until that condition is met you would not allow a player to use the casting tablet ?
That depends on the ritual on the casting tablet and the Virtues and Flaws of Octavius, of course. If Octavius does not have Faerie Magic, and if the ritual requires it (e. g. because it has Faerie Magic range, duration and/or target), by RAW Octavius cannot cast it, even with the help of the casting tablet.
A SG or the troupe can in the special case consider Octavius' Strong Faerie Blood as a limited substitute for Faerie Magic - but this would then be specific to the campaign.
Cheers
Serfs parma, but IIRC Faerie magic states that it allows the magus to use the faerie magic RDT. So, someone without Faerie Magic cannot use these specific RDTs.
Xavi
Has a matter of fact it was a season spell called "a season under the waves".
@Xavi : It prevents him to learn or create the spell (the distinction is slight i know) it's at the end of the paragraph about faerie magic in the core rulebook.
Doogy, you edited your post while I was already answering it. So I need a second post to answer the additions you made in the meantime.
I can't follow you here. Reading it up on ArM5 p.92f I find:
I can't follow you in this either. Are you referring to research that Quendalon (or the faerie posing as Quendalon) made after returning from his trip to the bohemian forest?
Let me explain further. By "non-standard spell resulting from an experiment" I referred to a spell that was the result of an experiment in the sense of ArM5 p.107ff Arcane Experiments. I would consider the spell on the casting tablet from LoH p.27 one of these. Such spells you can indeed learn from lab texts of their inventors. if you understand those lab texts, that is.
If the experimenter used Faerie Magic, you are stuck again with:
So there is a clear distinction here between spells just being the results of Arcane Experiments in the sense of ArM5 p.107ff, and spells invented using a Virtue like Faerie Magic.
Cheers
I'm the author of that section in Covenants.
I had no intent either way. I didn't even think about the issue. The rules as written seem to allow it, though my personal inclination in my game would be to allow it in some cases and not in others, with Mysteries sometimes required.
On a broader note, I'd like to remind you that asking authors for definitive rulings is outside the etiquette of this site, because the correct ruling is the ruling which you and your players agree to at your table, and because this is a conversation forum and asking for author-definitive rulings excludes the other participants, or at least makes their contributions to a discussion seem less valued.
Please don't use the thoughts of the authors to argue from authority in your own discussions. That's not how the game is intended to work.
I, for example, prefer to play Ars without dice, and the thing I'm working on for my next game starts in 221B Baker Street, so my opinion on things should never be taken as a definitive guide to the best sort of play for your table.
Sorry for the confusion because of my edit 
Learned not cast, so i would say that this goes toward the "you can cast with tablet" conclusion.
Indeed, and everything that you could create with the original/ancient magic research rules, I think i remember that it is implied that you can share Breakthrough point by sharing laboratory spells you created to achieve them but neither you or your sodales have the virtue (if any) that you will gain at the end. That would mean that you can share them before having the virtue with your breakthrough but not after.
Yes there is, in the casting not the learning, as I read it :
Spell result of experimentation (random happening/Original research) : You can learn it with no problem and cast it form tablet.
Spell result of invention through virtue : You can't learn it, you can cast it from tablet, you can get insight from the tablet.
The author could have written :
"Magi who have not learned the spell may use a casting tablet instead"
So, I see that some rules imply that you can't but others imply that you can (it's stated that a magus does not have to understand the spell to cast from a tablet) and the "researched in the lab" could be refering to the research for the virtue, not the spell as a spell is created not researched (if i recall correctly).
@Timothy Ferguson : Sorry if I offended you or did something I shouldn't have done and thanks for taking the time to come and answer my question anyway.
I was kind of told that my player conned me and that I made a mistake allowing it, that upset me more thant it should have 
I didn't want to use you as authority, just to know what you intended (if any), that don't mean that I will change the way I will use the tablets.
Giving the ability to cast spells you couldn't otherwise is a very cool feature of the casting tablet in my opinion and I love them this way.
This is always a nice place to start.
Well, that's kind of crass. I don't particularly care for casting tablets myself, but if a player or players found an ingenious way of using them, I wouldn't outright ban them, unless it was a house rule discussed at the start of the saga. Going further into this con, to use the term. I do hope the player is forced to go back to the well, so to speak, to use the spell again to solve some ongoing problem, if so, the con is still on. If so, the odds are against him from the experience leaving him unscarred. Consider he rolls a 0 on his casting roll. How many botch dice for the vis in this ritual? And then go to page 90 of Covenants and refer to the casting table. I do hope it is a suitably high level spell[1], like 35th level, because then you can stack on 7 more warping points. Of course, the Twilight experience should be suitably faerie in nature...
IMO, this is the only way I would use them as a player. The risk for messing with them is too great, otherwise. I'd do what I could to learn the spell or convince another player better suited to the Arts required for the spell to learn the spell.
[1]Personally, I consider a spell to have botched should be included in that -31 or less; or botch, but it's technically not RAW.
Well, he spent one full season creating the spell, an other one mastering it, and a last one creating the tablet : all that for a spell he can't use himself.
But with this spell Gwydion was able do go underwater with some of our covenfolks and investigate the demise of the "pic de lear" covenant in the middle of the Channel who was attacked by a powerful magic creature. He did this because he knew that the source of the aura on the site was the jail of his half-sister and dauther of lear (an ancient Ex Merinita maga who had succefully performed the ritual of becoming) whom he freed. He is now trying to help her regain her status in the order 
Rules need to be read in context. I mentioned already, that ArM does not list all that is impossible with a rules option - so you have to argue by what is explicitly allowed, not what is explicitly forbidden, when finding out RAW. I had also already given you the necessary context for that:
This says nowhere, that characters without Faerie Magic could cast spells with its special Ranges, Durations, and Targets. Access to these is gained only by "Initiates of the Outer Mystery" of Faerie Magic, unless a SG invokes ArM5 p.114 and allows them into a normal formulaic spell (which would bring us from RAW to - very legit - campaign specific rules), or another book - so far not yet found - allows them to other characters. The last phrase "Spells created ..." is only there to stress, that one also needs the Virtue Faerie Magic to learn spells with Faerie Magic R/D/T from lab texts.
This is an extremely creative reading of:
So if a magus - after becoming a faerie or being replaced by one - provides an initiation giving access to certain R/D/T, takes that initiation and then invents some spell, that all goes into a casting tablet another magus can use? I read "laboratory research" in the above quote as that standard lab research from ArM5 p.94ff the casting magus can do, considering his Virtues and Flaws at the time he uses the tablet.
In ArM5 rules spells are not learned from scrolls, but with the help of lab texts researched in the lab. Anyway the stress lies on the "instead".
Cheers
I cannot learn the spell because I do not have faerie magic, OK. Can I spont the spell then? I have not learned it, after all.
Since fae magic is the only thing that would allow me to use those RDT either in sponts or formulaics my own answer is a "no", but I think my troupe (that are lurkers around here and will use this against me sometime, I am sure...) would agree to it under certain circumstances. Like a tablet specifically designed to be used by non-faerrie magic magi. Be sure that this would imply concentration rolls and silly performances by the magi, just for the enjoyment of the local faeries. But as a general "grab a faerie spell tablet and off you go without problems" I would say "no".
Xavi
I disagree with that, the rules about the casting tablets tells you everything you CAN'T do with one : change the vis used or the arcane connection type, modify the spell in anyway. When a rule doesn't give you a direction, you can go any way most of the time it's common sense and others is troupe decision. In that specific case I didn't ask "is there anything allowing you to use casting tablet to cast a spell you don't have the virtus for" i asked "Is there anything in the RAW preventing someone from casting a spell..." and the answer as far as the exemples you gave me is no.
There isn't anything that explicitly allow you to do so either but (and that is my own interpretations of the breakthrough rules/exemples and casting tablet) there are evidence that you can cast spells without having the virtues that would allow you to create/learn them.
I did not read anything in the rulebook saying what is not explicitly allowed is forbidden, but as i told you before i see your point i just don't agree.
That is a great argument and i must say it's pretty convincing, but i would say that when you spont a spell you invent it on the spot
But you are right, by my logic it would be ok to spont the spell 
and I wouldn't allow that.
[EDIT] Hey you almost fooled me spont is explicitly banned to non faerie magic user ! you scoundrel !
---The next part go beyond the question---
A magus doing original research has spells he shouldn't have before finalizing his breakthrough and he can cast them. He couldn't have leraned/created them without the insight. If Quendalon created the FAerie MAgic virtue the same way that means he could cast spells with faerie range/duration/target witout having the virtue.
IIRC Casting tablets are NOT in the core book. As such it is fairly normal for Faerie Magic not to refer to them. I would treat them under the same terms as spontaneous magic unless the tablet was explicitly prepared to be cast by total nerds with no knowledge of faerie magic.
My position coincides with the one better expressed by OneShot, which I'll try to summarize as follows: the rules as written for casting tablets, taken in context, strongly suggest that tablets are meant to bypass only the work in the lab necessary to invent a formulaic or ritual spell.
A point slightly against this position is indeed that if a magus makes some laboratory Discovery during Original Research on some Hermetic Virtue, the non-standard spell incorporating the Discovery can be written down in a tablet and used by anyone. The way I see it, however, is that some aspects of the Original Research are immediately understandable to a "vanilla magus" (and can be in fact used as a leaping point towards the full understanding), but the full understanding that would come with the Virtue, and is necessary for most effects requiring the Virtue, cannot in general be "compressed" into a casting tablet. This is the reason why the magus embarking on Original Research cannot choose which "partial results" will come out of it.
I would simultaneously point out that OneShot's view allows for very clean cut decisions, whereas taking the opposite view opens up all cans of worms. If you allow Virtues to be "imported" into casting tablets, would a tablet for a Ritual written by a magus with Mercurian Magic allow the caster to spend only half the usual vis?