Limits of magic
Overview
Magic has many fundamental limits that restrict what can be achieved. In the setting these limitations are well known - magicians have striven for centuries to find ways to overcome them. Some people have devoted their entire lives to researching these limits, but no-one has ever found a reliable way to overcome them. Having a good working knowledge of these limitations is one way you can represent your character being a skilled practitioner of ritual magic.
In the game, these are most of the absolute limits of magic that is possible within the rules for the game. While you might play a character that is striving to overcome one or more of these limitations, it is important to appreciate that that is not possible in the Empire game. Any arcane projection that attempts will automatically fail. For that reason, it is a good idea to check any arcane projection against these limits before you submit it.
Restore Life
The Spring realm is powerfully resonant with healing magic, but no Imperial magician has ever been able to create a ritual that restores life to the dead. Some Winter magics allow a magician to contact the recently departed, or even summon back a shade that can be questioned, but like the Spring realm it appears to be powerless to help those who have passed on. In Empire, once a person dies, they are dead for good.
Many magicians have spent their entire lifetime searching for ways to cheat death. None have ever found a way to restore the dead to life, but a few have found ways to cheat death, or at least postpone it for a while. Although there are no rituals of this kind in Imperial lore at this time, anything like this would definitely need to be cast on the target while they were still alive.
There are rituals that allow a magician to give a semblance of life to a corpse, the most famous of which is Quickening Cold Meat. However these rituals work by conjuring creatures from the realms, usually drudges, to inhabit the corpse and cause it to move. The Winter realm has a strong affinity for magic involving dead bodies, but rituals of this kind make use of the body to house a spirit of the realm, they do not restore the body to life in any way.
Resist Effects
It is possible to use the Winter realm to create wards that harm those who cross them, and Night magic can hide the true nature of something, but beyond this there are few if any rituals that can offer protection to a subject. No magician has ever been able to create a ritual that allows the subject to resist a magical effect such as that caused by the repel spell. Nor is it possible to use ritual magic to make a subject immune to the blows of swords, bows, or other weapons. There are many rituals that make a subject stronger, allowing them to suffer more such blows before they are defeated, but none that make it so that the subject can resist or otherwise ignore the effect.
Mind Control and Silence
Many rituals create powerful emotions, feelings, or sensations in those that experience the effects, either as a side effect of the magic or as the main purpose such as with the Chamber of Pallas. These rituals can have a powerful effect on those that encounter them, but all serious magicians agree that the nature of the target's response is fundamentally set by them, not by the magician who performed the ritual. Magic is simply not powerful enough to control the mind of another living being, forcing it to act as the ritualist desires.
Of course there are ways to use magic to control your enemies, using it to threaten, cajole, and coerce people. However these methods are not intrinsically more reliable or powerful than a threat of violence. Skilled magicians can use ritual magic very effectively to influence others, but they cannot control them.
In the same way, magic cannot compel someone to speak the truth, and it cannot read minds. This means that there is no effective "truth detection" magic in the Empire. It is possible to create an urge to be forthright or plain speaking, but it is not even possible to create a roleplaying effect that makes a character want to speak the truth. Nor is possible to remove the ability to speak from a person using ritual magic.
One topic that comes up regularly with the Day eternals is that of magically summoned fortifications similar to Frozen Citadel of Cathan Canae but created in regions with the coastal quality. This matter is raised with some of Phaleron's heralds, and they provide the following explanation as to why it is not possible for magic to create such a thing. By its essential nature, a coastline is partway between one thing and another. It is a liminal space, neither land nor sea, and defies classification. A fortification or castle, by contrast, has an essential nature of resisting, standing strong, and being immovable and impregnable, which is absolutely at odds with the mutable nature of a coastal area. Ritual magic runs afoul of the Law of Essence, and so it will never be possible to create a ritual that conjures a magical fortification using the coastal quality.
From Hierarchs of sea and sky
Conjuring and Summoning
It is not possible to use ritual magic to force another being to appear before you, either a mortal or an inhabitant of the realms. There are Autumn rituals that allow you to send communications to another being, such as Call Winged Messenger, but the target is free to respond as they choose. They are under no compulsion to respond and they would need to use methods of their own to appear if they were far distant at the time.
Likewise, there are rituals that allow you to contact certain named eternals, such as Swim Leviathan's Depth. Some of these rituals create an opportunity to meet with the being at a regio later. Almost always, the eternal will appear as requested, but it is well understood that the ritual itself does not compel the being to appear, rather it is the nature of the eternal that causes them to act in this way. Having long ago agreed to respond if called, they are bound to do so for all time by their nature, not by the ritual itself.
It is possible to create rituals that request or invite inhabitants of a realm to enter the mortal world - albeit only with their agreement - but it is not possible to summon them. Rituals like Knights of Glory work because Eleonaris has agreed to release her knights into the mortal world when called. Likewise, rituals that attempt to create, conjure, or summon fortifications, citadels, or other structures from another realm will not work without the agreement of an appropriate eternal. Frozen Citadel of Cathan Canae works because Cathan Canae has many frozen citadels - which she sends to the mortal world in response to the ritual.
There are rituals that appear to breach these limits, such as Forge the Wooden Fastness or Dripping Echoes of the Fen where the eternal in question was not recorded for many years. Knowledgeable magicians knew that there must be an eternal in question - such a ritual cannot work without the assistance or involvement of one - but for whatever inscrutable reasons their identity had remained secret. In recent history, the eternals sponsoring those two particular rituals were uncovered by scholars of the Unfettered Mind.
Teleportation
It is possible for magicians and others to move from the mortal world to a chamber, but they cannot travel on from there: they must return to the mortal world through the same door they entered by. It is not possible to move onwards from a chamber, nor to re-enter the mortal world in a different location. This limitation is a fundamental restriction of the magic of the realms - it cannot convey a magician from one place to another.
A ritual like Call Winged Messenger will convey a message to a target, but this ritual works by literally summoning a winged messenger from the Autumn realm to carry the message. It takes time for the message to reach the target; it does not travel instantly.
Interestingly, this limitation is violated by the power of the Sentinel Gate. The Gate is a magical item, and as such it is a thing of the mortal world only and does not draw on the power of the realms. Whether it is this that allows it to exceed the limits of ritual magic is unknown, but certainly all attempts to reproduce the power of the Gate using ritual magic have always failed.
Invisibility
Although Varushkan folklore is replete with stories of wolves that are invisible, undetectable to the mortal eye, most magicians consider these tales fit only for a child. There have been countless attempts to use Night magic to render an individual invisible, but none have ever succeeded. The Night realm can mask a thing, change its shape or appearance, but it always leaves something in its place. There is no realm that can be used to make something invisible.
Although Night magic resonates with glamours that change the physical appearance of something, as well as rituals designed to baffle divinations, it cannot hide itself. If an army is enchanted with a Night ritual to conceal it then a divination like the Eye of the High Places that is lower magnitude than the shroud will still reveal that there is a Night enchantment in place. Similarly, it is not possible to use Night magic to baffle a ritual divination so completely that it returns the wrong answer.
Enchanting Bourse Resources
Mithril, white granite, weirwood, and ilium are the most precious resources found anywhere in the Empire, so valuable that control of known deposits is closely regulated by the Imperial Bourse. Countless attempts have been made over the centuries to develop ritual magic that can increase the production of these resources, but all have failed. Even attempts to scry for unworked deposits have proved unsuccessful.
Urizen magicians who have studied the problem for many years have concluded that materials of this kind have a degree of raw magical power inherent in them. This power appears to be a fundamental part of the mortal world, rather than having any connection with the realms. When the materials are in their unworked state waiting to be harvested, they create an interference that confounds any attempts to use the magic of the realms to locate or gather it. Sadly this natural resistance to magic is largely lost when the materials are removed and refined or processed.
So potent is this natural effect, that it has on occasion proved useful. The deposits of white granite in the Brilliant Shore were discovered centuries ago by a young icewalker who took shelter in the area while the region was assailed by a magical storm conjured by the Thule. When the magician noticed that the storm passed over the cave where they were sheltering, they realised that something in the area must be weakening the curse. Further investigation of the cave discovered the white granite deposits, and provided the Wintermark people with a valuable resource.
Supernatural Effects
Magicians can use the magic of the realms to change the mortal world, but it has an inherent tendency to resist this change. The more unnatural the change, the greater the resistance. One way that a magician can create a completely unnatural effect is to bring some force or object from the realms into the mortal world. Powerful rituals like Quickening Cold Meat summon Winter spirits to inhabit corpses so that they follow the magicians' will. The fortress "created" by Frozen Citadel of Cathan Canae is in fact one of the many that exists in the Summer realm and the ritual brings it into the mortal realm for a season.
Experienced magicians appreciate that the best approach is to create magical effects that work with the essential nature of the target rather than trying to create something unnatural. If a magician wishes to burn a forest down, it is infinitely easier to create a forest fire than it is to create a rain of fire.
Armies and Battles
It is possible to use magic that enhances the effectiveness of an army - either by requesting magical warriors from the realms to fight alongside them or by enhancing their strength, insight, or bonds. Cursing armies is possible, but is difficult and crucially requires a powerful arcane connection to the army in question - usually the general of the army or a similar figure.
It is not possible to curse an area or an army so as to impede army or navy movement in any way. Ritual magic cannot, for example, stop an army or navy moving into, out, or through a territory, nor restrict how far armies can move if they start in or move through that territory. It is not possible to use ritual magic to pin an army in place.
It is possible to use magic to affect a territory to increase or decrease the number of casualties that result in from any fighting. Rituals like Rivers Run Red and Rivers of Life affect everyone in the territory in a way that makes them more or less likely to die. What is not possible is to use magic on a territory to directly affect the outcome of a three month long campaign in that territory. Strategic outcomes are too complex and too unpredictable to be influenced by magic in this way.
You can create magic that influences the fighting - you might fill an area with storms for a season - but that does not affect the outcome of the campaign, i.e. it does not affect the victory points assigned to either side. No matter how potent the magic on the territory, it will be indiscriminate, and that means it will create effects that both sides are able to take advantage of based on whatever actions they take.
You can create rituals that enchant or curse armies - to make them more or less effective. But any ritual that attempts to enchant or curse a territory with the goal of positively or negatively influencing the outcome of a military campaign that takes place there will fail.
Economic Territory Effects
It is not possible to use ritual magic to duplicate the effect of a great work - that is, to increase the production of all resources of a specific type in a territory.
Seasonal Stacking
The ritual enchantments Blessing of New Spring, Strong Ox, Golden Sun, and Gathering the Harvest have a unique synergy that allows each to build on the other. It has proved impossible to duplicate this synergy with rituals intended to be cast on resources other than farms - the rituals remain peculiar anomalies.
Transmutation
It is not possible to turn most personal resources into a military unit using magic without the direct aid of an eternal. To be transformed, a resource must have some kind of innate magical power, either a mana site, a forest, or a mine. You cannot transform businesses, congregations, farms, herb gardens, military units, or fleets.
Imperial Citizenship
It is not possible to use ritual magic to sever the connection between a person and an egregore. The connection seems to be protected by the Law of Essence. A person can voluntarily choose to give up their connection to an egregore, but this choice cannot be forced using magic.
Sharing Ritual Lore
While rituals such as Shared Mastery of the Magician's Guild allow a coven to share spellcasting knowledge between its members, it is not possible to do the same with ritual mastery. While ritual magic can remove mastery (as seen with Infant Starts with a Blank Slate), it can never grant someone mastery of a ritual.
Meta Magic
It is not possible to use ritual magic to affect other rituals. There is one ritual in Imperial lore, Sign of Aesh, that can be used to reduce the magnitude of a later ritual, but that is deliberately restrictive and not something possible to replicate on a larger scale. It is also not possible to use a ritual to affect the casting time of a different ritual.
Changing Qualities
It is not possible to use ritual magic to change the qualities of something - whether that be the special quality of an army - or the unusual qualities of a region or territory. You can't use magic to make a region coastal, or remove the haunted quality, or make an army cruel.