From The Cornerstones of Magic, by Priestess Istai (Formerly Elah Salliar)
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If there were to be a single spell which can be said to be solely responsible for modern spellcasting, it is Tabula Rasa, the Blank Slate spell. At risk of oversimplifying, it resets the local Tapestry to almost exactly the same condition every single time, enabling spells and rituals to be readily and repeatedly cast far, far easier than historically was the case. It is the first spell cast in any ritual, serving as the foundation of the rest of the working.
Under normal circumstances, magical echoes may linger in any confluence of mana, be it a spell, power, or even natural eddy. This can cause unpredictable tangles and snarls of mana that can throw off any but the most brute-force and simplistic abilities. This is why nearly all external magics for magical creatures are simple expressions of an elemental phenomenon, be it a shield, lightning bolt, or cloud of darkness. Anything more complex simply requires more setup than a natural ability could feasibly assure, and even then retains a high risk of catastrophic failure (Divine magics, such as that of the Blessed, are a literally miraculous exception, but will be studied in due time). This is of course thanks to the precision to the nearby Tapestry which learned magic relies upon to work change upon the world.
In antiquity, it was only truly feasible to use rituals through very specific setups, such as during astronomical events like a Twin Day, which floods the world with enough magic as to functionally wash away all minor perturbations and enabling consistent casting during these events. This is thus why so many rituals require a powerful confluence of magic in some form or another.
While some Elven traditions utilize the natural propensity they possess for magic to enable yet force them to manually account for any slight perturbations in the Tapestry, grand rituals atop a volcano, during a grand thunderstorm or earthquake were the only true method of ensuring a modicum of reproducibility, and thus casting, learning, and utilization of magic.
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Tabula Rasa was first developed by High Archmage Alara Ethluil approximately six hundred years hence, by studying the manner in which spells impacted the Tapestry. At the time, magic was thoroughly unexplored, subsiding largely upon the ritual scraps still known past the collapse of the Old Empire.
A few of what we would today call druid cabals existed, sharing what few secrets they possessed among their members, all located at natural ritual points, such as the ever-mentioned volcanoes, enchanted glens, and stormy isles. Their magics were potent in the places it could exist, but did not travel well. Coupled with their natural secrecy and magedom was very much considered to be the realm of the hermitical and outcast. Even in those locales wherein society could safely form a town around a ritual point (without seriously disrupting the local Tapestry, as happened often with forest-based sites), magic remained an elusive and secret art, occasionally melding into the noble class (in such cases where spells were practical enough for political leverage) or remaining an underground cult.
More mundane magic still abounded, of course. Witches still used Flare variants to light their cooking fires and small gusts of wind to remove dust from counters, alchemists utilized finicky, unreliable rituals and spells to refine their ingredients, and village healers called upon the gods to heal the sick and wounded. Ikraish grew at this point, leveraging the ability to trade magical goods despite the Tapestry this close to the ocean being far too chaotic for ‘traditional’ casting methods.
Due to their unreliability, such household charms were rarely explored with any real regularity and were often considered wastes of time and curiosities, often not even worth bragging about even if one could truly call upon their magic. Usually, it was a skill for the house-tenders to master, spinning thread and learning a few basic cantrips to aid around the house.
Alara Ethluil was one such witch, a housewife born with the talent to see the Tapestry. She used this ability to expand her magical repertoire from the absolute basics, able to use the eddies and calm spots of the Tapestry to cast her spells far more reliably than any of her peers. Driven by incredible curiosity, she poked and prodded her magic, watching how spells influenced and were in turn influenced by her magic. Over the years, this grew and developed as she learned how best to chain multiple spells together, priming and eventually setting off a magical effect far more complex than a single spell could manage. However, Ethluin magic was not truly born until she created the Tabula Rasa, enabling all of her spells to be cast quickly, consistently, and with almost no chance of failure and making her the first mage.
With few willing to actually learn magic from her, she instead experimented in private and with her children, gradually becoming more and more adept at spells. While without tools she was incapable of casting any rituals quickly, she was more than able to fulfill her personal duties with a mere single spell or two a day, the hours a foci-less ritual takes not a true obstacle for her.
Once Tabula Rasa became more widespread, it swiftly came under the exclusive purview of first the nobility, then mages altogether as the more familiar limits of magic became apparent to them. This new breed of mage remains the predominant school to this day, though the modern Tabula Rasa is of course substantially more refined than Ethluil’s original spell, being faster, easier, and less tiring to cast.
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Now, Tabula Rasa is not a perfect spell. It does little, for example, against the massive magical confluences that wiped clear the Tapestry for the ancient mages. Water magic will always be more prevalent proximal to the ocean, life mana more prevalent in a forest, and fire mana more common around a volcano. Furthermore, it does not keep the mana calm, merely overrides it momentarily. Further casting will of course disturb the mana, interfering with future spells unless a new Tabula Rasa is cast or the snarls are accounted for in some manner.
It is, however, very flexible in its affected area. While older versions of the spell uniformly wiped an area of the Tapestry clean, the modern Tabula Rasa may be cast to precisely include only the area in which the spell is constructed, usually near the caster’s hand.
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It is worth noting that Tabula Rasa from different individuals are not wholly identical. It, like all magics, varies ever so slightly with the precise mana possessed by the mage. In many ways, they even outright conflict unless the mages are specifically trained to work together (as is occasionally the case with close partners), but it is of course possible to learn to cast in another’s Tabula Rasa, as evidenced by apprentices who need to do just that for the entirety of their apprenticeship until they are dubbed a full Mage and learn the spell themselves.
For multi-mage rituals, it is often the case that a single individual is designated the caster and maintainer of Tabula Rasa, as it is far simpler to learn how to make a single spell function within another’s Tabula Rasa than it is to make multiple castings of the spell work together. It is theorized to be related to the nature of the caster’s soul, and is what results in nearly all mortal mages possessing such similar Tabula Rasa, for all that ‘similar’ still prevents sensitive magics from functioning.
It is usually believed that part of what allows sorcerers to be so skilled with their selected element is that their soul has in some way changed to reflect their magic, but that assertion is hardly proven. It is an undeniable truth that the Tabula Rasa of a pyromancer is less conducive to water magic as that of a hydromancer, just as the reverse is likewise true, yet there are many possible alternative explanations.
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While it may seem as though spell staves bypass the normal requirement of utilizing Tabula Rasa to cast their spells, this is in fact very untrue. One of the principle purposes that the foci serves is acting as a continuous cleanser of the Tapestry, functioning as its own Tabula Rasa in addition to acting as a supplement for the rest of the casting. It is not, of course, an actual Tabula Rasa, and while different scribes may utilize different methods, one of the more common is to magically isolate the interior of the focus from the exterior.
In this way we can begin to understand a portion of how the Tabula Rasa truly functions. Like the mages of old, the normal chaos within the Tapestry prevents delicate spellcasting, but under a suitably powerful magical force, the disturbances do not vanish, but are instead washed away. However, unlike the mages of old, Tabula Rasa is both portable and usable under any circumstances, as well as not carrying any inherent elemental bias beyond that of the caster, leaving such matters to the primer spells, thus making it an excellent base for any type of casting.
This is, of course, what leads to the joke that Fireball is a Tabula Rasa for pyromancers, and while this is not strictly false, neither is it properly true. The simple fact of the matter is that most spells simply do not possess the power to wipe clean the Tapestry with their mere existence. Mages are not limitless fonts of power, unlike a volcano or ocean. Spells are limited, weak, and many spells are indeed designed to have a minimal impact upon the Tapestry, Fireball included.
The reasons for this is twofold: First, energy spent affecting the Tapestry is energy not spent changing reality. Second, impacting the Tapestry with a cast spell decreases the amount of time required between actual Tabula Rasa castings. This latter reason is of course related to how counterspells function, and indeed the Counterspell most commonly in use was derived from very similar principles as Tabula Rasa.
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There are, naturally, many opportunities in which a Tabula Rasa is not required for spellcasting. As mentioned earlier, ancient mages did not possess the spell and so relied on naturally occurring stable (or at least consistent) areas of mana. Some modern mages have even replicated that feat within their towers, utilizing an unknown method to permanently enchant their tower to maintain a continuous Tapestry-cleaning effect, making all their own magics much simpler to utilize. It is, however, often believed to be tied to casting in the same location for decades and may simply be the result of sheer practice.
Similarly, some internal magics do not require a Tabula Rasa, the spell already adequately sheltered by the soul and thus requiring far less in the way of external shielding.