Proffejor

I noticed on my last reading of Words of Radiance some references that led me to this same conclusion. The following points may help back up your story, although I do not have specific quotes at the ready. Pattern flat-out tells Shallan that she can change souls at one point. He elaborates saying that soulcasting is different for her because she can "...make lies into truths" instead of just changing physical objects because of the interplay between lightweaving and soulcasting. Early in WoR, she draws Tvlakv's driver, Bluth, and he behaves very differently after that point, although we are led to believe that he was enamored of the version of himself from the picture she drew, it is likely she just re-wrote his personality. Later, she mentions that all of Vathah's men had a drawing made, and each becomes fiercely loyal to her, and even Gaz runs errands and does carpentry for her, which is out of character for the weasel-y little cyclops. More interestingly to me, though, after her first meeting with The Ghostbloods, she marvels at how she was able to escape as Veil. She says she felt like another person, which leads me to believe she may have soulcast herself into a competent thief, for a time. An apropos theory about how the Archive may conclude.

Excellent. Thank you for your help in testing my theory (and disproving it.)

The Ghostbloods could have given Lin Davar the information of how to turn his daughter's spren into a soulcaster, if they had such knowledge. The may even have made him agree that it would become theirs after his death, and he might have agreed, if it was the only way he saw to save his house. Lin takes a blade from his daughter, and later has a soul caster. The blade he takes is actually a Spren that can manage the surgebinding of Soulcasting. Is it so far to go to think he was told a way to make the Spren into a Soulcaster by the Ghostbloods? If I am right, they had Lin Davar convince his daughter to give up Pattern in a similar way the Knights Radiant gave up their shards. This left Pattern as an inert blade that could be bound into the Soulcaster, which I contend is a specific shape that can bind liespren inside, making them function as the go-between into Shadesmar to deliver Stormlight and convince objects to transform. This is still just a theory, but one I like toying with.

I agree that the knights wouldn't think it okay, but I assume that ALL Soulcaster fabrials were created at a similar time as the Shardblades were made. Before that time, people WERE soulcasters, and they started showing up before each desolation, so soulcaster fabrials weren't needed as a tool. The ancient Knights didn't trap the spren, they just left the spren as shards and the shards faded and weakened. In Dalinar's vision he sees more shards than he calculates may exist in present day Roshar. What if a large portion of those discarded blades were turned into Soulcasters by people in the next century? Not all blades would be suitable of course, only Liespren or Shadowspren could be made into Soulcasters, but soulcasters are useful tools. If I am correct, if any Surgebinder was to make contact with an actual soulcaster that contained a bound spren, instead of a false one, or a broken one, they would hear screams in their heads as those that contact Shardblades do.

This is true. I am making the assumption that the Ghostbloods would lie about having owned the Soulcaster originally, as admitting that they had a hand in making it would bring disaster if it came to the attention of the church. Jasnah was targeted by the church, largely because she (seemingly) had a soul caster. I think her Heresy would have been an unfortunate quirk of the noble line if she did not seem to possess a soulcaster that threatened their monopoly. I imagine that the way that Shardblades are "made" of the corpses of Spren, and the imprisoning effects of the soul caster would be related. It would be surprising if it did not require some action on the part of the surgebinder, as Sil, The Stormfather, and Pattern have all referenced acts of surgebinders going towards "killing" them. I believe that it will come to be shown that a certain action by a surgebinder will weaken a bonded Spren. This has already been hinted at in Kal's relationship with Sil. I think Shallan did something, likely at the instruction or machinations of Lin Davar, based on a script written by the Ghostbloods. This act hurt Pattern the same way Kaladin harmed Sil in WoR. Perhaps it was as simple as killing her mother. This might have made Pattern into an inert shard blade, which Lin was able to place in the safe until the Spren could be bound into a soul caster. Perhaps, in the safe itself was an empty Soulcaster prison waiting to accept the Spren that Shallan had bonded with, given to Lin by the Ghostbloods. Soulcasters are an intricate pattern of chains and gems, and it makes some sense that a weakened liespren may be comforted by being in a shape with a regular geometry, even if that shape is actually a prison. The largest supposition I feel that I make is assuming that the Ghostbloods would have the knowledge of how spren bonds work better than the spren themselves have. It does make sense to me that this may be the case, but there is admittedly little evidence to support this.

I would imagine that the creation of new Soulcasters is like the creation of new Shardblades, unheard of in current Roshar. The understanding has been lost, as people haven't bonded Spren of any kind since the recreance. The existing Soulcasters in Roshar would all be ancient hand-me-down Fabrials from that time. This seems corroborated by things from the books such as Kabsal telling Shallan that Alethkar could declare war on Terravangian if he took Jasnah's Soulcaster. If a new ones could be created, there would be a market for them, even if the Vorin church strived to keep them rare. I even think that Navani mentions that creating new Soulcasters has eluded artifabrians at one point.

The answer is no, as stormlight is the power source. But Pattern may still be what made it function.

I have a theory that may might need some scrutiny. The Soulcaster Shallan has in The Way of Kings was cut, and it stopped working. What if the soul casting fabrials are just prisons that hold a Spren capable of soul casting? Maybe I am overthinking, but it seems to me that all Soul Casters would need to contain some form of intelligence that could exchange Stormlight in Shadesmar to effect an object's change into one of the ten essences. Shallan is an intelligent human that could not convince a stick that it wanted to be fire, so we know that the objects can be willful, if not stubborn. Either there exists some trick to force a soulcasting, or an intelligence must present an argument to convince the object to change. If this is true, a Lightweaver's Cryptic could potentially be bound into a soulcaster for others to use, without needing to have a bond. Soulcaster Fabrials are a delicate pattern of chains and gemstones. I imagine them as a web of delicate lines with gemstones interspersed. What if they function as a web and hold a spren in between the cognitive and physical realm? Shardblades are the remnants of a broken bond and a formerly bound spren in some form of agony, which is why those sensitive to a bond can't touch blades without hearing the screams. It does not seem unlikely that Soulcasters are similarly remains of Spren, but in a more active capacity. If this is true, then cutting the soul caster might free an imprisoned spren. We are told that Shallan did not attempt to summon Pattern as a blade after the death of her mother, due primarily to that trauma. She Imagines that the blade is imprisoned in the safe in her father's study. But this does not explain fully why the Cryptic was never visible to her until the events in The Way of Kings. (Assuming that the pattern she is looking at on the ceiling of her quarters before she first heard the "What are you?" question was actually the Cryptic.) Why did Pattern seemingly not appear to a young Shallan after the death of her mother as she was growing up? It's possible she just wished him to leave her alone, but then why dld he come back later? Could there be a procedure that would have allowed her father to bind Pattern and create a Soulcaster fabrial? If the Ghostbloods knew of an ancient secret like this, and found that the Davar daughter had a bonded spren, possibly because her mother talked about her child's supernatural nature while looking for a "cure", it does not seem impossible that they might offer Brightlord Davar the method, and use of the resulting fabrial, in exchange for his allegiance. Perhaps a young Shallan would rationalize an event like removing her bonded spren as her father taking her blade, and putting it away in a safe. It always seemed incongruous to me that Lin Davar, portrayed as an ambitious man who would do almost anything to get a stronger position, did not attempt to gain anything from his daughter having a shard blade. I realize that the Radiants were looked at with scorn, and that it is possible he did not want his House tainted by their memory, but would he have not looked into how the shard blades of the past were separated from their owners originally? It would have solved multiple problems at once. Would questions along these lines eventually lead him to the Ghostbloods? If he somehow took advantage of his daughter after finding out she was bonding a Cryptic, and manipulated events so that he could get a soul caster made from the Spren, that would seem to me to be more in keeping with his character. Pattern lost his memories at the time of Brightness Davar's death, possibly because his bond with Shallan was weakened by her wanting nothing to do with him, and, at the same time, Shallan went mute and became antisocial, presumably due to guilt. I propose that Brightlord Davar somehow took Shallan's spren after the death of his wife, and used knowledge gained from the Ghostbloods to imprison Pattern and create a fabrial for exploitation. I also think that the forced breaking of the bond was what damaged Shallan's young mind and fractured Pattern's memories. Are there any holes in this theory that I am overlooking?