In PST, one of the most distinct things about the githzerai is their speech pattern. They place a heavy emphasis on 'knowing' the world around them, and commonly use metaphors and historical references in their words. So! Small complication of those I could find. Note that most of these are said by Dak'kon, and I will specify if they are said by someone else. If I missed any, feel free to add them!

• "Ach'ali Drowning" - Said by Dak'kon when hurt.
  • Ach'ali was a foolish githzerai who drowned in the sea of Limbo after asking so many useless questions that her focus, and shelter, collapsed in on her.
• "As twisted as Fri'hi's roots" - A complicated matter.
  • Could not find any information of Fri'hi.
• "Hashma's folly" - To cheat, specifically used in the context of cheating in a bet. Said by Gaoha.
  • Could not find info on Hashma. It is also the name of an Egyptian sand-stone but I doubt that's what the writers were referring to.
• "Hail, sword ringer" and "Zerchai's kin bow to you" - common greetings, to which one responds "And the traveler is pleased".
  • Could not find any information on Zerchai.
• To be as "Rrakma's Jewel" - In agreeance on a situation, specifically used in reference to the anarchs and zerths being in agreeance on Dak'kon's exile. Said by Kii'na.
  • Rrakma, usually spelled as Rrakkma, are githzerai war bands that hunt down illithids. Could not find information on Rrakma's jewel.
• "Tachia's Folly" - Exact meaning unknown, said by Dak'kon when rolling a critical miss.
  • I could not find any information on Tachia, but seems to be Dak'kon reprimanding himself for a lack of discipline. I'd guess Tachia had made some foolish mistake similar to Ach'ali.
• "T'cha's choice" - A situation where you have no choice/only the illusion of choice.
  • Could not find any information on T'cha.
• "Their cupboards are bare" - Something said of a generous person
• "Vilquar's Eye" or "Vilquar's heart beats in your chest" - To accuse another of treason. Latter saying is from Kii'na.
  • Vilquar was an enslaved gith who acted as a spy for the illithids, only to be consumed by them once Zerthimon tricked him into thinking he'd won.
• "Wrote the book of Anarchs" - Said in reference to a person being wise.
  • Anarchs are those in githzerai communities responsible for maintaining stability in the chaotic plane of Limbo.

In the Planescape: Torment, one of its most influential and iconic writings is the Unbroken Circle of Zerthimon - the retelling of life and death of the githzerai's most important prophet and martyr, Zerthimon. This document is carried by Dak'kon, a devotee of Zerthimon. At some point in his life, Dak'kon suffered a crisis of faith when he came to doubt the intentions behind Zerthimon's action nearing the end of his life. The idea that his faith and society could have been built on a lie distresses Dak'kon deeply, and only by discovering Zerthimon's true intentions is he healed of his mental strife.

However, at the end of the game, its revealed that the circle was written by the Practical Incarnation. It calls into question which parts are real and which parts are fabrications, which is what I want to analyze.

Short Explanation:

I believe the first six circles are accurate to githzerai legend but the Practical Incarnation wrote the last two.

Long Explanation:

Part 1: The Unbroken Circle of Zerthimon

The Unbroken Circle of Zerthimon is a githzerai religious text recounting the compelling and tragic story of a man who suffers greatly to protect his people from their slavers (the illithids) and later from themselves. It was given to Dak'kon in game by the Practical Incarnation, a previous form of the game's protagonist, the Nameless One.

https://preview.redd.it/0c6js6ujp7hh1.png?width=1497&format=png&auto=webp&s=dad9b8a034fb60ae5e69f50f48954f7afb787fae

​I assume you've all read them, but if you need a refresher you can read all eight circles here. For the sake of this post, I will summarize the relevant ones.

• The Third Circle of Zerthimon tells the story of Zerthimon suffering torture at the hands of his slaver, the illithid Arlathii Twice-Deceased. Zerthimon was believed to have accepted this punishment on the Pillars of Silence to hide the fact he was a part of the rebellion against their oppressors. 
• The Fourth Circle of Zerthimon tells the story of Vilquar. He acted as a double agent for his illithid slaver, pretending to be an ally to Zerthimon but working against him in secret, resulting in many deaths. Upon discovering his treachery, Zerthimon silenced the uprising and tricked him into believing he had won. Vilquar expected a reward from the illithids, but once his usefulness ran out, they consumed him, allowing the rebellion to remain in secret. 
• The Fifth and Sixth Circles tell the story of Zerthimon meeting Gith, an intelligent and charismatic rebel who he ended up following. The fifth circle tells of their meeting, describing that Zerthimon was incredibly infatuated with her as a speaker and leader. However, they grew apart due to philosophical differences. The sixth circle describes their falling out and the beginning of the civil was – Gith wanted to lead a complete genocide of the illithids and to establish their own empire, Zerthimon wanted their people to abandon the war and heal. The war that ensued allowed the illithids to survive Gith’s wrath

Part 2 - Dak'kon's Crisis

Dak'kon was once a highly respected Zerth, a disciple of Zerthimon who acted as a leader in the community, until his own doubt destroyed him (Possibly due to different reasons than the crisis this circle gave him, but it is relevent). While it is unclear the process one has to go through to become a zerth, we understand they act similar to priests in githzerai communities. I think we can assume that Dak'kon has likely studied the history and teachings of Zerthimon outside of the circle The Practical Incarnation gave him.

If the Nameless One becomes a mage, he can learn the teaching of Zerthimon by reading the Unbroken Circle of Zerhthimon. Despite being written in the gith's circular Tir'su, the Nameless One is able to understand the words (which could mean nothing).

A bit of nuance you don't get from reading the text alone is that the story of Vilquar is somewhat glorified among the githzerai. They believe that his treachery was a necessary evil that allowed lulled the illithids into a false sense of security that allowed the gith to act when the right time came.

https://preview.redd.it/ttajpx8np7hh1.png?width=1167&format=png&auto=webp&s=20c2a1b6cac75a06f34a60c655e882773da60a7e

​What Dak'kon came to believe is that this story of Vilquar was used as propaganda. That by pointing out how treachery is sometimes necessary, good even, it lays the groundwork to justify Zerthimon preventing Gith from committing complete genocide against the illithids. He begins reading into the story of the third circle and theorizes that perhaps Zerthimon didn't have his people's best interest at heart.

https://preview.redd.it/oe3nw9iop7hh1.png?width=1500&format=png&auto=webp&s=fdaf119f6105c012b5f3ef5b38db5d3df5ee9f0a

https://preview.redd.it/f9ok5bhpp7hh1.png?width=1487&format=png&auto=webp&s=40dc60b32f019ff2d055e62b32f09e89dc021a7b

​The idea that his messiah, a man whose life he spent preaching the philosophy of, was a puppet of his race's slavers is something to no ones surprise deeply distresses Dak'kon. As a result, it affects his ability to use wield Karach blade, a sword made of Limbo's chaos matter tied to its weilder's emotion. Kii'na, another Zerth you meet, comments his karach is as thin as a mist. Honestly the karach blades are much cooler than later editions making the githzerai unarmed monks and i will stand on that hill.

https://preview.redd.it/gg5v2dprp7hh1.png?width=1512&format=png&auto=webp&s=5c8fa8d11fde951354cef0313618d559d0b5b166

However, if the Nameless One is able to study the circle further, he is able to discover something Dak'kon hasn't. With an intelligence of 19 and up, he is able to rearrange the six circles and discover two more. These do not continue the story, merely describe Zerthimon's moral teachings.

• The Seventh Circle is a parable telling the importance of patience. The upirising of the enslaved Gith did not happen all at once, it happened through small victories that built up over time.
• The Eighth Circle is a parable about how doubt can destroy a person's will. If one does not truly believe in what they are doing, they must act to change it, even if it leads them to suffer.

Discovering the truth is what restores Dak'kon's faith. In finding Zerthimon truly did have his people's best interest at heart, his mind is healed and his doubt is cleared. Happy ending, right?

Part 3 - Where It All Goes Wrong

This nice character arc comes crashing down at the end of the game when you meet the Practical Incarnation, the version of the Nameless One to give Dak'kon the Unbroken Circle of Zerthimon. You find out he created the circles with the intention of making Dak'kon a more powerful minion.

https://preview.redd.it/hr64cadtp7hh1.png?width=1520&format=png&auto=webp&s=4320e1bd238d6b058788574cad8e32a47cf1c2a3

https://preview.redd.it/gp8oviuup7hh1.png?width=1506&format=png&auto=webp&s=08fc968154e283a89228ac0e8856b99b45e0274e

Part 4 - Is it all fake?

I often see people on this subreddit insist that the entire story told must be fake. I've even seen some go as far to question if Zerthimon himself was a real person. Undoubtably, this revelation makes the entire story questionable. I mean, the practical incarnation calls it 'a collection of lies', right? But I feel its a little more complex than that when analyzing other interactions in the game, Dak'kon's history, and the Practical Incarnation's history.

From a meta perspective, the strongest argument for the circles being true to canon is that the first and sixth circles align with every recounting of gith history at the time - their people were enslaved by mindflayers for generations, a woman named Gith rallied them together and led a massive slave revolt, but Zerthimon came forward at the end to oppose Gith's imperialist desires and died in the ensuing conflict, becoming a martyr to his people.

1. “In githzerai lore there is a central figure that is revered above all others — Zerthimon. The githyanki believe him to be a great god that was once a man. According to githzerai lore, when the original race broke free of the mind flayers, it was Zerthimon that opposed Gith, claiming that she was hateful and unfit to lead the people. There ensued a great battle and the people were polarized by the two powers. Those that chose to support Gith became the githyanki. Those that supported Zerthimon became the githzerai. Zerthimon died in the battle, but in his sacrifice he freed the githzerai from Gith.” – Outer Planes Appendix for the Monstrous Compendium, 1991 
2. “Originally, their ancestors were humans enslaved by the evil illithid race. But at a point in the far distant past, they were led to freedom by a great female warrior named Gith. But upon gaining that freedom, the people immediately became divided. According to legend, a man named Zerthimon stepped forward to accuse Gith of being unfit to rule the newly freed slaves. Gith, Zerthimon said, was evil and would lead the people to ruin. A great battle was fought between the two factions, in which Zerthimon was killed.” – Planes of Chaos Boxed Set, 1994 
3. “When Gith ordered her people to continue their campaign to annihilate the illithids and establish an empire of conquest of their own, not all followed her command. A new figure, by the name of Zerthimon, had gained a significant following and challenged Gith’s plans and her leadership. Gith was evil, the newcomer claimed, and would lead the people into darkness and tyranny not unlike the illithids themselves… Zerthimon was killed and his followers, now called githzerai, retreated to Limbo in defeat.” - A Guide to the Astral Plane, 1996

From an in game perspective, the characters and stories mentioned in the Unbroken Circle are mentioned by other githzerai. Firstly, the term 'Vilquar's Eye' is presented as a normal term of phrase among their people, along with multiple others that have no connection to the circles written by the Practical Incarnation.

https://preview.redd.it/b6uw1nfwp7hh1.png?width=1511&format=png&auto=webp&s=e7187a2ae1a8c92f57075e440ab90b72822dfc73

When speaking with Kii'na, who we can assume went through a similar process to become a zerth, we see this in action as she compares Dak'kon to Vilquar twice in the same conversation.

https://preview.redd.it/c8np23hyp7hh1.png?width=1510&format=png&auto=webp&s=6ce3949f6c790a4ff4af3b6cf2f0b5a32fadd410

https://preview.redd.it/c0fpw1azp7hh1.png?width=1516&format=png&auto=webp&s=3c1f567df40b57eca5944f6feecb62ebd877a42f

Keep in mind that Vilquar is not some one off mention, it's one of the most important stories to Dak’kon’s arc. The fourth circle is the catalyst for his crisis of faith. He believed that by glorifying Vilquar’s betrayal of Zerthimon, their people glorified Zerthimon’s betrayal of Gith. It was the seed that planted his doubt.

https://preview.redd.it/4jpfy4g0q7hh1.png?width=1510&format=png&auto=webp&s=77d77a40b45e78c58618ca4e48af28114f315083

https://preview.redd.it/36w75rb1q7hh1.png?width=1502&format=png&auto=webp&s=a964b316dbef27646c3987d123b868ec59f61f17

If the circles were fake stories written by the Practical Incarnation, there is no way Kii'na would have referenced them. Firstly, the Pracical Incarnation gave the circles to Dak'kon after the sacking of Shra'kt'lor, so he couldn't have taught her that story before being banished. Secondly, she does not recognize the Nameless One, so he didn't teach it to her himself. Thirdly, non-githzerai are not allowed inside Shra'kt'lor, so he probably couldn't have shown it to literally anybody in that city.

https://preview.redd.it/uf3lvhg2q7hh1.png?width=685&format=png&auto=webp&s=f59c30a27d8a79d47c850201c0accf6c7501da9c

https://preview.redd.it/d4q4qam3q7hh1.png?width=717&format=png&auto=webp&s=ffeb02b187d56ff4f87d62a9aed20d6df96a0c16

Additionally, I think it would be wildly out of character for the Practical Incarnation to simply make up stories if he was trying to manipulate a zerth. This is one of the most intelligent and diligent characters in the game. He planned every outcome of his goals years in advance and considered every angle of his plans. This is a man who spent months, if not years, manipulating a woman into falling madly in love with him, only for him to kill her and use that love to bind her to the planes as a guide.

The Nameless One can read the circle despite being written in Tir'su without even learning how to speak it. This means the Practical Incarnation would have studied their culture enough to have learned to read and write their language at an advanced level to even create the circle.

https://preview.redd.it/l4cljtz4q7hh1.png?width=1182&format=png&auto=webp&s=d89d139d0e2222e64fa268e5f9585602378c6cb0

I ask you: what is more in line with what we know about the Practical Incarnation - that he would use his intelligence and cunning to create the most authentic historical artifact he could, or that he would simply write his own RPF fanfic and hope Dak'kon, who has spent his whole life preaching Zerthimon's name, would just not notice?

What I believe is that when the Practical Incarnation says “Perhaps the words carry some truth – I know not.” he isn’t saying “Idk, I just made that shit up” and more “I didn’t go out of my way to verify the authenticity of Githzerai legend.”

Part 5 - So... is it All Real?

I would argue the same answer as the first. It's complicated. The practical incarnation does refer to it as being a collection of lies, so where can we draw the line? Which circles are canon, which aren’t?

We need to keep in mind the Practical Incarnation's goal with his writings - clear Dak'kon's mind of doubt in Zerthimon. This was obviously not done out of the kindness of his heart, the karach blade Dak'kon wields is tied to his emotion and mental state. He was attempting to tell Dak'kon what he wants to hear to make him a better fighter.

What I believe are entirely false are the seventh and eighth circles. Firstly, Dak'kon, despite being a zerth, has never seen these circles or heard these teachings, which is suspicious as hell.

Secondly, these are the circles that accomplish the practical incarnations goal. After reading the final circle, Dak'kon's stats become boosted, as well as his sword. At high morale, he becomes a better spellcaster out of his desire to protect you, and at low morale he becomes a better fighter out of his desire to kill you.

Part 6 - Conclusion

The first tragedy of this theory is that the reinstatement of Dak'kon's faith was a farce and he'll never know. So much happens after the party is split in the endgame, the Nameless One never gets a chance to tell Dak'kon the truth before dying and (possibly) being resurrected in the endgame.

Potentially though, it leads to a darker conclusion. If the historical accounts in the Unbroken Circle are true, but the moral teachings are false, this opens the possibility that Dak'kon could have been right about Zerthimon.

If Arlathii Twice-Deceased genuinely suspected Zerthimon was plotting to rebel against him, implanting orders that persist after his death is something the illithids are more than capable of. In fact, this exact scenario plays out in the 1998 adventure Masters of Eternal Night.

In this story, you explore a nautiloid that has essentially been frozen in time since the original illithid empire, and can fight alongside their rebelling enslaved Gith (referred to as ‘forerunners’). If you kill the illithids, two of the forerunners immediately turn on their leader Nilton due to psionic conditioning.

https://preview.redd.it/wa50o5kcq7hh1.png?width=775&format=png&auto=webp&s=e65a81106b7152833709123e4091bccab44c6171

Additionally, its sequel (also from 1998) Dawn of the Overmind also theorizes that genetic tampering could be the cause of the civil war.

https://preview.redd.it/avjxjwp7q7hh1.png?width=845&format=png&auto=webp&s=b81d6849d146ed08497b2e3440cb48502421cbf0

Now I'm not saying 'Gith did nothing wrong' here. The fifth and sixth circles make it very clear that she never broke free from the cycle of violence she was born into, and would have likely repeated many of the illithid's cruelties if she was not stopped. But it was the civil war that allowed them to escape the wrath of Gith, crippling her effort to destroy the illithid empire once and for all.

And what was the first thing the surviving illithids did upon escaping? Did they learn from their old ways and change as a society? No, they fled to Faerun’s Underdark and continued their ways, subjecting the Duergar dwarves to the exact same enslavement the Gith faced. The civil war very much ended in their favor.

But I digress as I am straying away from PST analysis and getting into fanfic territory here, so:

MY FINAL VERDICT

Circles 1&6: Canon because they line up with previously established lore

Circle 4: Canon because it is referenced by other githzerai

Circles 2,3&5: Mostly canon because Dak'kon would have recognized major embellishments in his own peoples history

Circles 7&8: Probably written by the Practical Incarnation