Please imagine the mental image of a slightly hyperactive Labrador gleefully fielding a thrown stick: the stick in question being profounddecisions.co.uk/empire-wiki/Ritual_theory.
cheering
First impressions:
Fundamental limits to magic. Excellent.
Experimentally derived laws for magic. Also excellent.
‘You can’t cross the streams’ isn’t in there explicitly, but may have been thought to be obvious; it’s certainly a logical consequence of various of the principles.
This is an excellent stick with which to provide consequences to experimental magicians determined to beat their heads against the laws of metaphysics until something breaks - and more than that, it’s a decent map to what is and isn’t possible.
Magical research is R&D, not bluesky research. You’re prototyping something that uses existing rules in a unique fashion, seeing if people will buy it, then getting investment and commercialising it. Here are the existing rules. There are some glaring things that these rules allow that don’t exist, and there’s plenty of room for market share. If you really like, I’ll provide 20 rituals I want, but most of them will look extremely boring 
PRINCIPLES:
Intent: what you wanted to do back when you wrote the ritual is important. If you push the bacon button, you get bacon. You cannot push it in a funny manner to get vegetarian bacon.
Presence: no action at a distance except as detailed below. No specific wording on whether a part of a thing is sufficient to enchant the whole thing, whether you can enchant someone if all you have is their severed hand or something, but this is a decent area to research.
Dominion: If you have the person in charge of something, that counts as Presence for that ‘something’. This is how the Anvil Regio works; this is how resource and army enchants work. Magic armies have a hack, and it’s a hack I really like: the general’s in charge of the army, and the army can fool the world into believing it’s in charge of the territory, so targeting the general hits the territory. Corrollary: I expect there to be rituals out there that require an Emperor/Empress.
Bonds: Magic spreads across bonds. Not usually strongly enough to count as Presence, but there are exceptions such as Crystalline Focus of Aesh.
Scale: There’s a sweet spot for any given effect in magnitude terms. Going with that sweet spot, if you can, gives you the most bang for your buck (except see below: more bang is possible). There’s a lower limit which I’m going to guess is 10-20% lower. Cheap plastic effects are cheap and plastic and you’re usually better off paying an extra mana for the proper version, but also it’s really really not worth going above that sweet spot unless you’ve got buckets of mana and you’re trying to enchant people with a rare set of abilities. Nothing we didn’t know already, but nice to confirm.
Transience: The sweet spot for enchantments is a season. Power falls off rapidly below that and magnitude less rapidly.
Synergy: The thinner you spread your buck, the more bang it produces. We knew this already: army and territory enchants are twice as good (or more) as small-unit and single-resource enchants, small combat buffs are twice as good as large ones. It’s a principle.
Boundaries: lines on maps mean something, not because of the line on the map, but because the people who drew the map put the line on the most meaningful boundary around there and THAT means something. This is why territory enchants hit just a territory.
Essence: magic that is more like something’s essential nature is easier; meanwhile the Hermetic Limit of Essential Nature from Ars Magica is right here. You can’t make something do something it can’t do, merely something it doesn’t have the strength to. The more unnatural your magic is, the harder it is - each Realm interprets ‘unnatural’ differently, see the Realm pages. You can overlap the material realm and one of the Eternal Realms to provide something significantly unnatural, but then that has its own essential nature to contend with.
LIMITS:
These things are impossible:
Restoring Life to the Dead
Immunity to the Actions of Others
Overthrowing the Will of Others
Conjuring and Compelling Appearance
The Teleportation of the Body
Invisibility
The Enchantment of the Three Fundamental Materials (I really need a better name than Bourse Resources)
The Limit of Essential Nature (I think that perhaps the ‘supernatural effects’ and ‘Essence’ limit and principle are better the other way around, so I’ve basically just included them both twice)
The Limits of Divination - lumped together into one, this looks like the shadow of a very thoroughly explored space. There are things divination can’t tell you. Look it up if you’re a diviner
BUT
Eternals can help you reach just that little bit further than you otherwise could. You can create rituals with their help: they are bound to them when they agree to them. My hunch is that they are exerting their will to mess with what the realm considers ‘unnatural’ to make these rituals exist.
ALSO ONE OTHER BIG CHANGE:
Eternal communication is now via prearranged channels only. This is an IC change. There’s something about most of the Eternals of a realm that are interested in business with the Empire going and talking to the Archmage of the realm and giving them a batphone with a certain amount of pre-paid credit. We’ll see what that amounts to in play, but my immediate guess is “If you are not getting your share of Eternal plot, BUG YOUR ARCHMAGE”.
