This subject came up in the Ranulf thread, I thought it was of interest to a broader audience than those choosing to follow development of my NPC.
I think that the guidelines are just guidelines. They're there to help set a level for spells and effects. Determining whether or not something that isn't clearly in a guideline is possible without research comes down to the art descriptions and to judgment on the part of the story guide.
I think that Ken's observation about the increasing necessity for guidelines is about how presentation changed over the line's run. When an author wanted to present somwthing different to be done with hermetic magic, they presented a guideline rather than just a spell. It isn't a question of guidlines being absolute requirements just how new stuff was presented. I guess you could think of it as guidelines being absolute requirements with the caveat that the set of things which can be done with hermetic magic, if expressed as a set of guidelines, is much larger than the set of guidelines that are printed in the game. When the game line printed spells that didn't fit an existing guideline, they presented a new guideline to describe it.
I would not restrict my players to the list of published guidelines. I'd use judgement (mostly), the art descriptions (a little), and the rest of what's published (a fair amount) to decide things.
I agree and I don't think the precedent of the Magic Realm guidelines from RoP:M is in conflict with this. Manipulating the Magic Realm is distinct enough from vanilla Hermetic Magic that it would not even be unreasonable to require a Virtue for it. Requiring a minor breakthrough to access all of these complicated guidelines at once seems seems quite fair. That doesn't mean one needs a breakthrough for every spell that deviates from printed guidelines even a little.
Indeed, you should avoid such generic restrictions.
Yes, some spells and devices published late even ran afoul directly of ArM5 p.111ff Spell Design rules, like HP (2012) p.82f Assassin's Bell: these require timely storyguide attention, so as not to annul a guideline with a published effect.
But it is exaggerated and quite destructive, to conclude from such examples the need to prevent all use of published effects as guidelines.
Many published spells wouldn't be possible if every spell needed to conform with a published guideline. This also holds for spells published verrry late, like in TtA (2015): ArM5 p.160 Wizard's Communion does not conform to any guideline published ever, and TtA p.75 Wizard's Vigil and TtA p.137 Day of Communion are still derived directly from that spell.
Storyguides are from the beginning explicitly given a lot of leeway to permit spells: see e. g. ArM5 p.114 Changing Ranges, Durations and Targets and ArM5 p.114f Requisites.
Using published spells as additional guidelines was also necessary from the beginning, and always required judgement: like with HoH:TL p.73f Aura of Inconsequence.
In general, the purpose of the guidelines published later is, to fill gaps and provide rules to invent more types of spells, rather than to retrofit guidelines onto spells already existing.
A few of the more notable things that pop up for the use of existing spells vs spell guidelines include the ones mentioned in Ranulf's thread: the MuAq spells giving liquids a solid or semisolid state without the use of Terram requisuites. (If you haven't read that thread, it's a blast.) Another that came up recently is The Severed Limb Made Whole, which has a -1 magnitude for the limb being already present.
Definitely a house rule since the core book explicitly allows using those examples. There are some listed exceptions, such as alterations to Aegis of the Hearth. But the general rule as stated in the core book is that you can build off the examples there, and many of the examples use guidelines that are not listed in the boxes. One Shot already noted Wizards' Vigil and Day of Communion that I was thinking of among others.
I'm not sure where this is coming from. There are many examples of spells without guidelines listed, including spells in the supplements. Yes, guidelines have been added frequently, but nothing that would logically indicate this, especially considering the core book disagrees with this as well as a number of example spells presented in supplements.
This fits the written rules perfectly.
This can also fit the rules perfectly because of that caveat, which essentially turns it into your prior statement that also fits the rules.
Also to note the guidelines constrain spontaneous magic more than formulaic spells which are more constrained than rituals.
When a spell is slightly more powerful than the guideline, stick to the guidelines when doing spontaneous magic. Formulaic magic is a little more flexible.
Can you explain what you mean here in a different manner? I often don't bother too much with guidelines for spontaneous magic in play but only because I don't want my players to have their noses stuck in the rule book rather than what's going on in the story. Is there some text that tells me I should be more flexible with sponts, or is that just how you think it works best?
There is the issue that special spell parameters can be used with formulaic spells but not spontaneous. That seems only tangentially related.
T Riffen Rex wrote that spontaneous magic should be less tightly constrained, by guidelines not more so . I brought up the spell parameters because parameters and guidelines are in some ways similar things and by showing that the constraints were tighter on parameters for spontaneous magic I hoped to show why I didn't follow his view on guidelines.