So, I get tired of the lack of historical info on Sima Yi. Most of what I've found has been filled with more fiction and folklore than fact, and has come from less-than-credible sources. From what I understand, Sima Yi's official biography in Wang Yin's Jin Shu is really long and nobody has the time or patience to translate it. Fair enough, I know I certainly couldn't do it.
So to try and help those who are interested in historical* information regarding Sima Yi, I've compiled and paraphrased various passages of Sima Guang's Zizhi Tongjian.
* Given Sima Yi's status as grandfather of the founder of the Jin Dynasty - which wrote most of the records referring to him - even official histories must be viewed with skepticism.
Edited by Zyzyfer
Sima Yi (Zhongda)
Sima Yi was the younger brother of Sima Lang [from Henei], who served as Prefect of Yuancheng and then Master of Records to the Chancellor [Cao Cao]. 
When Sima Yi was young, he was said to be intelligent and ambitious. Cui Yan praised him as having clear intelligence and an understanding of justice.  He also noted that Sima Yi could make “firm decisions” and possessed “exceptional bravery.” When Cao Cao heard of this evaluation, he offered Sima Yi office. He was made Senior Clerk for Literary Scholarship.  In this manner, he became a member of Cao Cao's civil administration in 208.
There are several stories that involve Sima Yi initially refusing Cao Cao's offer of employment. All of these stories follow the same basic structure: Cao Cao [or an agent thereof] becomes aware of Sima Yi's abilities and offers him a position. Next, Sima Yi refuses and pretends to be ill. Finally, Cao Cao threatens to imprison Sima Yi, so Sima Yi agrees to serve him.  Such stories are almost certainly folklore; writers of the time knew that the Jin Dynasty [founded by Sima Yi's grandson] destroyed the Wei Dynasty [founded by Cao Cao's son] and could not resist the idea of Cao Cao forcing Sima Yi to serve him, thus bringing about his eventual downfall. While there are accounts such as this in official histories, they should be viewed with extreme skepticism. It is worth noting that Sima Yi's eldest child, Sima Shi, was also born in 208, and it is entirely possible that this was a reason for any hesitation on Sima Yi's part.
To provide a balanced summary, it is best to say that Sima Yi joined Cao Cao after some initial hesitation in 208 after being recommended by Cui Yan.
After joining Cao Cao in 208, Sima Yi advanced through the ranks of the civil and military bureaucracy. Seven years later, by 215, he was Master of Records [zhubu]  to the Chancellor [Cao Cao]. 
Following the surrender of Zhang Lu to Cao Cao in 215, Sima Yi urged Cao Cao to invade Yi Province. At that time, Liu Bei was in a dispute with Sun Quan regarding ownership of Jing Province, and Sima Yi believed that Cao Cao could take advantage of Liu Bei's absence and the resentment of the recently-conquered people of Yi in order to seize the province. Cao Cao rejected his advice, fearing that he would overextend his army if he invaded Yi at that time. 
Even though Cao Cao did not take Sima Yi's advice regarding Yi Province, he still respected Sima Yi's abilities. By 219, Sima Yi held the position of Major [sima]  to the Army of the Chancellor [Cao Cao].
In 219, Guan Yu was besieging Cao Ren at Fan City in Jing. Furthermore, he had sent a detachment ahead to Jia County, only 80 kilometers from the capital, Xu City.  Because enemy forces were so close, there was some discussion about moving the capital. Sima Yi advised Cao Cao against relocating the capital, arguing that Guan Yu's military forces were not worth considering – their only major success had been because of good luck, therefore he was no threat to the capital. He further argued that Sun Quan and Liu Bei held deep grudges against each other, and that Cao Cao should ask Sun Quan to attack Guan Yu's rear, and make him king of all the southern lands if he agreed.  Sima Yi's advice proved its worth soon after. Sun Quan sent Lü Meng to attack Guan Yu. In the end, Guan Yu was killed.
Later in 219, Cao Cao considered relocating his population along the border with Sun Quan and Liu Bei [in Jing]. After the attacks by Guan Yu earlier that year, he was afraid that they would defect or flee to Sun Quan. Sima Yi advised against this, saying that those who would have made trouble had fled into hiding at the death of Guan Yu. As a result, the only people Cao Cao could move would be those who were already loyal to him. Moving them would make them resentful and distrustful, destroying their loyalty. And the disloyal ones who already left would find their suspicions confirmed and would never submit to Wei. Cao Cao agreed with his logic and did not relocate the population. It is said that, later, those who had fled returned to Cao Cao's territory. 
Sometime between 219 and 224, Sima Yi was made one of the Masters of Writing [shangshu]. 
In September of 224, Cao Pi left Xu City and led his army south to display it before Sun Quan in hopes of frightening or beating him into submission. Sima Yi was stationed at the capital during this expedition.  The expedition ended without fighting and Cao Pi returned to the capital, though he intended to launch another attack against Sun Quan in the near future.
In the spring of 225, Sima Yi received another promotion. He was made Grand General who Comforts the Army. When Cao Pi went south again, Sima Yi was again left in Xu City to oversee the documents handled by the Masters of Writing. 
In June of 226, Cao Pi became deathly ill, and appointed three officials to act as guardians and guide his heir, Cao Rui. They were Cao Zhen, Chen Qun, and Sima Yi.  Cao Pi died the day after entrusting the future of the state to those three.
In September of that year , Sun Quan invaded Wei. Sun Quan attacked Jiangxia, while Zhuge Jin and Zhang Ba attacked Xiangyang. Sima Yi led the army to Jiangxia first and drove off Sun Quan. He then attacked Zhuge Jin and Zhang Ba. Zhuge Jin fled and Zhang Ba was killed. For his achievements in this campaign, Sima Yi was promoted to General of the Agile Cavalry [biaoji jiangjun ]. 
In the beginning of 227, Cao Rui conducted a rearrangement of his administrative structure, promoting a number of officials and generals. Sima Yi was promoted to Grand General of the Agile Cavalry. 
In July of 227, Sima Yi was appointed Chief Controller [dudu] of Jing and Yu provinces, and was in charge of all military affairs in those two provinces. He was stationed in Wan, one of the largest cities Wei controlled in Jing province. 
Earlier, in 220, Liu Bei's general Meng Da had defected to Wei.  He had been put in charge of Xincheng and served Wei during Cao Pi's reign. He had many friends in the upper administration. By 228, many of them had passed away, and Meng Da's loyalty wavered. He decided that his fortunes might be better in Liu Shan's army, so he sent letters to Zhuge Liang pledging his loyalty to the Liu faction once again. The Wei officer Shen Yi  learned of these communications and reported the matter secretly to the court.  According to some sources [namely the Wei Lue ], this memorial was ignored, although this is likely a dramatic embellishment, as it would be strangely negligent for Cao Rui to ignore such a warning, particularly as Meng Da commanded an important border city.
Meng Da learned that his changed loyalties had been reported to the court, so he prepared to revolt openly. Sima Yi – aware of Meng Da's plans thanks to Shen Yi's memorial – sent a letter to Meng Da. It read:
"Formerly you, General, left Liu Bei and entrusted yourself to our state. And our state has given you a frontier post, thereby entrusting to you the measures of our plans against Shu. The purport of our state is as bright and pure as can penetrate the sun. [The men of Shu, both wise and foolish], all have been gnashing their teeth at you. Zhuge Liang wishes to destroy the plan, but lacks the wherewithal. Guo Mu's mission is not a trifling matter; how can he make a light issue of it and divulge it? This is, I think, easily understandable."
This letter caused Meng Da to hesitate, and he delayed his plans to openly rebel. While Meng Da was hesitating, Sima Yi gathered his troops and marched in secret. This march was made with stunning speed. According to Meng Da, Sima Yi's base at Wan was 800 li [around 260 miles] from Luoyang, and 2,200 li [around 730 miles] from Xincheng. Given the distances involved, Meng Da calculated that, before Sima Yi could take action against him, Sima would first have to secure approval from Cao Rui, a process that would take almost a month. By that time, Meng Da was confident that his city would be secure. Reinforcements from Zhuge Liang would have arrived and the walls would be fortified. Sima Yi, however, decided not to wait for prior approval from Cao Rui and forced a rapid march to Xincheng, covering 2,200 li in only eight days. Liu Bei and Sun Quan sent reinforcements to Meng Da, and they marched to Mulansai and Anqiao, respectively. Sima Yi sent generals to hold them back while he surrounded Xincheng.  Sima Yi besieged the city for sixteen days and captured it, after which he executed Meng Da. 
Very shortly after that, Shen Yi carved an Imperial Seal and began to give titles to people. Sima Yi summoned Shen Yi and arrested him, sending him to Luoyang. 
In August of 228, Sun Quan ordered Zhou Fang, the Grand Administrator of Poyang, to lure Cao Xiu into their territory so Sun Quan could defeat him. Zhou Fang sent a letter to Cao Xiu saying that he had been banished and wanted to surrender Poyang to Wei. Zhou Fang acted the part of a condemned official and Cao Xiu believed his letters. When Cao Xiu advanced to receive Zhou Fang, Sima Yi was sent to Jiangling and Jia Kui led troops to Dongguan so that they would be in a position to support Cao Xiu should the need arise.  Cao Xiu fell into the trap and was defeated. Though Jia Kui ultimately rescued him , Cao Xiu died shortly thereafter of wounds he suffered during the fighting. 
Earlier in 228, before Sun Quan's success against Cao Xiu, Zhuge Liang invaded Wei for the first time.  Though he met with some initial success due to the commanderies of Tianshui, Nan'an, and Anding revolting in his favor , his forces were defeated in battle at Jieting  and Jigu , leading to his retreat back into Yi Province. The commander of Wei's defense, Cao Zhen, anticipated that Zhuge Liang's next attack would be at Chen City, so he sent the veteran general Hao Zhao to repair the walls and garrison the city.  True to Cao Zhen's prediction, Zhuge Liang attacked the city shortly after Cao Xiu's defeat by Zhou Fang, but he was unable to overcome Hao Zhao's defenses, and retreated again.  In 229, Zhuge Liang sent Chen Shi to attack Wudu and Yinping commanderies. The defender of the region, Guo Huai, withdrew to defend more vital territories, allowing Chen Shi to reclaim some territory the Liu faction had lost during Zhuge Liang's first campaign. 
In 230, Cao Zhen wanted to pursue an offensive strategy against the Liu faction. Sima Yi and others were sent to advance with Cao Zhen into Yi Province.  Unfortunately, heavy rain began to fall and it washed away the roads, keeping Cao Zhen and Sima Yi from advancing.  Following the advice of several officials, Cao Rui ordered Cao Zhen to withdraw.  Sima Yi and Cao Zhen withdrew without actually fighting any of Zhuge Liang's soldiers.
In 231, Zhuge Liang invaded Wei again, surrounding Mount Qi.  Cao Zhen was ill, so defense of the region was given to Sima Yi.  Specific accounts of the battles that followed are generally unreliable , but a basic summary of events is as follows: Zhuge Liang attained success over some Wei generals at Shanggui, where he was then able to harvest the wheat to supply his army for a little while.  Sima Yi's general Guo Huai was able to use his influence with the local tribes to ensure that Wei's army had plenty of provisions in spite of the setback at Shanggui.  Zhuge Liang withdrew to Mount Qi and established camps there. The Wei army engaged in battle with forces led by Wei Yan, and Wei Yan was victorious.  Shortly thereafter, Zhuge Liang retreated due to a lack of supplies. Zhang He pursued the retreating army but was killed in an ambush. 
Zhuge Liang was heard from again in 234 when he made his fifth – and last – incursion into Wei. This time he coordinated with Sun Quan to invade Wei on two fronts.  While Zhuge Liang advanced into Yong Province, Sun Quan set his sights once again on Hefei. Zhuge Liang paused at Mei, south of the Wei River. Though most of his subordinates wanted Sima Yi to remain north of the river, Sima Yi pointed out that there was a great deal of food south of the river and he did not want that to fall into Zhuge Liang's hands, so Sima Yi crossed the river and built fortifications to resist any enemy attacks.  Guo Huai expressed to Sima Yi the concern that Zhuge Liang would seize Boyuan, which would cut Sima Yi off from the rest of Wei. Sima Yi sent Guo Huai to defend the position. True to Guo Huai's prediction, Zhuge Liang led an attack against Boyuan, but Guo Huai repelled him.  Because his advance was thwarted, Zhuge Liang settled into position at Wuzhang and started growing crops to feed his army, preparing for a drawn-out engagement.  Meanwhile, Sun Quan sent large forces against Hefei, Xiangyang, Guangling, and Huaiyin.  Believing that Sun Quan's attack was the greater danger, Cao Rui personally went to oversee the fighting at Hefei.  Cao Rui sent reinforcements to Sima Yi and instructed him to wait for Zhuge Liang's provisions to run out, then attack him when he retreated.  Shortly thereafter, Man Chong and Cao Rui attacked Sun Quan's army and forced them to flee. 
What exactly transpired regarding Sima Yi's standoff with Zhuge Liang at Wuzhang is unclear due to conflicting accounts from several sources.  It seems clear that Zhuge Liang tried to entice Sima Yi to fight on several occasions, and that Sima Yi declined to engage him each time.  Allegedly, Zhuge Liang sent Sima Yi a bonnet and women’s clothing in an attempt to enrage him, thus convincing him to fight; however, given the source of the story, this is unlikely to be true.  It is further stated that Sima Yi requested permission from Cao Rui to fight several times. Though Cao Rui refused to give Sima Yi leave to attack Zhuge Liang, he feared that Sima Yi would not listen, so he sent Xin Pi to urge restraint from him.  Zhuge Liang is said to have remarked that Sima Yi's request to fight was only to make a show for his army, and that if he truly saw some advantage in engaging Zhuge's forces, he would do so whether he had permission or not. 
Allegedly, Zhuge Liang sent an envoy to Sima Yi's camp  and Sima Yi questioned the man about Zhuge Liang's habits. Learning that Zhuge Liang ate little and oversaw countless small matters personally, Sima Yi surmised that he was going to die soon.  While their armies were still at a standoff, Zhuge Liang did indeed pass away. 
The story of what followed is, again, obfuscated by differing and unreliable accounts. One story tells that Zhuge Liang's Chief Clerk, Yang Yi, led the army in retreat, and Sima Yi pursued. When Sima Yi was near, Yang Yi turned the army around as though to fight him, and Sima Yi retreated. 
Another account says that Zhuge Liang gave Yang Yi, Fei Yi, and Jiang Wei secret orders to lead a retreat following his death. These orders were not made known to the veteran general Wei Yan. When Yang Yi began to lead the retreat, Wei Yan went ahead of them and destroyed the roads to prevent the army from withdrawing so that they could continue to fight Sima Yi. In the end Yang Yi and Wei Yan fought, with Yang Yi emerging victorious and Wei Yan being killed. 
The first account of events has Sima Yi retreating from an enemy in flight without giving battle, while the second features Zhuge Liang's army fragmenting and fighting itself. It seems more logical that Sima Yi would be willing to let the enemy army destroy itself and felt no need to become involved, thus he did not engage the enemy. Regardless of which account seems more reliable, both come to the conclusion that the invading army retreated following Zhuge Liang's death, and that Sima Yi allowed them to do so without a battle.
In 235, as recognition for his defense of the state, Sima Yi was made Grand Commandant [taiyu]. 
Now, many years earlier, in 190, Dong Zhuo appointed Gongsun Du as Grand Administrator of Liaodong. There, Gongsun Du established himself as a king, dividing Liaodong into various commanderies and taking many imperial honors for himself – he all but declared himself independent from the Han.  During the years of turmoil that followed in central China, many fled to Gongsun Du for protection.  In 204, Cao Cao made overtures of friendship to Gongsun Du, offering him the title of General Who is Firm and Majestic and enfeoffing him as Marquis of Yongning. Later that year, Gongsun Du died and was succeeded by his son, Gongsun Kang.  In 207, after suffering many defeats at the hands of Cao Cao, Yuan Shang, Yuan Xi, and many Wuhuan leaders fled to Gongsun Kang for protection. Gongsun Kang killed them and sent their heads to Cao Cao, thus cementing friendship between the two factions.  When Gongsun Kang died, his sons were both very young, so his brother, Gongsun Gong, took over the affairs of Liaodong. In 228, Gongsun Yuan took control of Liaodong from Gongsun Gong.  In 232, Gongsun Yuan made a deal to sell horses to Sun Quan.  Because he was making contact with the state's enemies, Cao Rui sent Tian Yu and Wang Xiong to attack him. They accomplished nothing, and Gongsun Yuan became distrustful of Cao Rui.  In 233, Gongsun Yuan feigned surrender to Sun Quan, and killed several envoys that Sun Quan sent to him. 
So, the Gongsuns had a long and complicated history with the Cao faction. Gongsun Yuan was insulting to Cao Rui's envoys and angered Cao Rui with his exploits against Sun Quan. In 237, Guanqiu Jian asked permission to campaign against Gongsun Yuan.  Cao Rui assented, but Guanqiu Jian met with no success. Guanqiu Jian fought Gonsun Yuan at Liao River and was defeated, withdrawing to Beiping. Gongsun Yuan formally rebelled and called himself King of Yan, and enticed the northern tribes to harass Wei. 
In 238, Cao Rui summoned Sima Yi from Chang'an and gave him an army with which to invade and pacify Liaodong. 
The reason the Gongsuns had managed to maintain their independence for so long was because Liaodong was difficult to invade. Any army would either have to sail there on boats or cross through the mountains. Additionally, Liaodong was simply too far from the court, so anything that happened there was rarely reported to the capital. It was nearly impossible to bring supplies or reinforcements to fight against a defensive force in Liaodong. 
Before Sima Yi set out, Cao Rui met with him and asked him what Gongsun Yuan would do. Sima Yi said that fleeing would be Gongsun Yuan's wisest option. Otherwise, he could defend certain key positions, or focus on defending his capital city of Xiangping. The last one Sima Yi considered his worst option. Reasoning that Gongsun Yuan would not be wise enough to flee, Sima Yi predicted that Gongsun Yuan would defend positions along the Liao River and then pull back to Xiangping. All things considered, Sima Yi reasoned that the campaign would take one year. 
In the sixth month of 238 [May 31- June 28], Sima Yi arrived in Liaodong. True to Sima Yi's prediction, Gongsun Yuan sent his Grand General Bei Yan and Yang Zuo to build camps along the Liao River, where they prepared to resist Sima Yi's advance.  Sima Yi's officers urged him to attack Bei Yan and Yang Zuo, but Sima Yi did not want to waste soldiers attacking fortified positions. Instead, he send a small force southwards with many drums and banners, making that army appear far larger than it was. Bei Yan and Yang Zuo left their fortifications to pursue the decoy unit, so Sima Yi moved across the river and built some barricades, turning it into a defensible position.  Bei Yan and Yang Zuo realized they had been tricked and were worried that Xiangping – which was now only lightly defended – would be in danger. The two generals turned around and began marching home to Xiangping. They encountered Sima Yi's army in the night. Sima Yi was prepared for them, and the two were utterly defeated. He then advanced on Xiangping and laid siege to the city. 
Unfortunately for Sima Yi, the weather turned against him. During the seventh month of 238 [June 29- July 26], heavy rain caused the Liao River to overflow, flooding the area. The flooding was so intense that cargo ships could allegedly sail from the river to Xiangping. Because of this, the siege of Xiangping could not be completed. Some in the army wanted to withdraw to the fortifications by the Liao River. To maintain discipline, Sima Yi ordered that anyone who propagated the suggestion would be put to death. When one of his officers, Zhang Jing, violated this order, Sima Yi kept his word and executed him. 
Relying on the flooding to keep Sima Yi at bay, the locals were gathering firewood and grazing their herds without paying much attention to the army. Some of Sima Yi's generals wanted him to seize the livestock, but Sima Yi would not hear of it. One of Sima Yi's officers, Chen Gui, pointed out the difference between Sima Yi's lightning-fast destruction of Meng Da and his slower methods in dealing with Gongsun Yuan. Sima Yi explained that Meng Da's army was small but well-provisioned, while Sima Yi's had been large but without adequate supplies. Therefore, he had to be swift in suppressing Meng Da. In the case of Gongsun Yuan, the army was larger than Sima Yi's but had far fewer provisions, so it was best to be patient and starve them out. Sima Yi went on to say that his biggest concern was that the Gongsun army would flee and would have to be hunted across Liaodong. If Sima Yi plundered their animals and assaulted their civilians, it would compel the Gongsun leaders to flee. So, it was best to wait for their supplies to diminish, trusting that the flooding would keep them from fleeing – and would make them believe they could still flee if they decided to. Once the ground dried out, Sima Yi could complete the encirclement quickly and trap them completely. 
As soon as the rain stopped, Sima Yi completed his encirclement of Xiangping. He raised mounds, dug tunnels, and constructed ladders, assaulting the city swiftly and violently.  Gongsun Yuan ran out of food and some of his generals – including Yang Zuo – surrendered. Allegedly, his population resorted to cannibalism.  In the eighth month [July 29 – August 27], Gongsun sent two of his officials [Wang Jian and Liu Fu] to beg Sima Yi to raise the siege, offering that Gongsun Yuan would present himself as a prisoner if the army withdrew. Obviously, this was a bad deal for Sima Yi. He had no way of knowing if Gongsun Yuan would do as promised, and if Sima Yi withdrew his encirclement, Gongsun Yuan could simply flee. So Sima Yi executed Wang Jian and Liu Fu. He informed Gongsun Yuan that if he wanted to surrender, he would have to send more intelligent envoys with better offers. Gongsun Yuan then sent Wei Yan, who asked if Sima Yi would accept hostages. Sima Yi pointed out that he already held all of Xiangping hostage, so there was little purpose in accepting any specific individuals. 
In the ninth month, the remnants of Gongsun Yuan's army collapsed. Gongsun Yuan tried to break through the encirclement but was killed along with his son.  When Sima Yi entered the city, he separated the long-time rebels from those who had recently rebelled out of desperation. He pardoned the latter and executed the former, regardless of whether they were government officials, soldiers, or civilians. After witnessing the ruthless extermination of long-time rebels as well as the mercy shown to those who surrendered, all of the territories in Liaodong surrendered to Sima Yi.  He performed funeral rites officials who had been executed for opposing Gongsun Yuan, issuing them posthumoius honors and ordering that their tombs not be desecrated. Sima Yi also allowed everyone who had fled to Liaodong since 190 to return home without trouble. 
Around the end of 238, Cao Rui fell deathly ill and knew that he would die soon. He worried that his heir would not be able to govern on his own and wanted to appoint officials to guide him.  Initially, Cao Rui appointed the following officials:
* Cao Yu was made Grand General [da jiangjun]. He was one of Cao Cao's sons [Cao Pi's half-brother]. During his childhood, Cao Rui lived with Cao Yu. 
* Xiahou Xian was appointed General Who Guides the Army [lingjun jiangjun]. It is not clear which branch of the family he was from.
* Cao Shuang was appointed General Who Guards the Military [wuwei jiangun]. He was the son of Cao Zhen.
* Cao Zhao was made [dunji xiaoyu]. His father was Cao Xiu.
* Qin Lang was made General of the Valiant Cavalry [xiaoji jiangjun]. He was one of Cao Rui's generals and enjoyed the emperor's personal trust. 
There were two officials who handled confidential matters for Cao Rui, named Liu Fang and Sun Zi. They were at odds with Xiahou Xian, Cao Zhao, and Qin Lang, so they plotted to estrange those three from Cao Rui.  Cao Yu declined the position, believing that he lacked the skills necessary to guide a ruler.  Cao Rui began to doubt the abilities of the other officials he had selected and asked Liu Fang and Sun Zi who would be able to do the task. They recommended Cao Shuang as well as Sima Yi.  Cao Rui vacillated over the decision but ultimately took their advice. He dismissed Xiahou Xian, Cao Zhao, and Qin Lang from office.  Sima Yi was summoned and Cao Shuang was appointed Grand General [da jiangjun]. Because Cao Rui feared that Cao Shuang was not competent enough for the position, he appointed an officer named Sun Li to be Cao Shuang's Chief Clerk [changshi].  Cao Rui sent a messenger to urgently summon Sima Yi to the capital.  Previously, Sima Yi had been given orders to return to Chang'an by the quickest route. Having now received two different orders, he hurried the the capital to find out what was happening. 
Sima Yi arrived in the beginning of 239, shortly before Cao Rui's death. Cao Rui entrusted Sima Yi with the guardianship of his heir, Cao Fang. Cao Fang embraced Sima Yi.  At this time, Cao Fang was only 8 years old. 
It should be clarified that Cao Rui had fathered no sons. He adopted Cao Fang as well as Cao Xun in secret and raised them as his children. The name of Cao Fang's true father is unknown.  It has been suggested  that Cao Fang's father was Cao Kai . Another potential candidate is Cao Yu or his son [name unknown]. Cao Rui was raised in Cao Yu's household and clearly felt a great affinity for Cao Yu. It would not be unfeasible for him to make Cao Yu's son or grandson his heir. Given the ages of the parties involved, it would likely be the case that Cao Fang is the grandson of Cao Yu, if they are related so closely.
When Cao Fang took the throne, Sima Yi and Cao Shuang were both given the title chizhong , giving them responsibility for the appointment of local officials and for nominating officials for civil service. Also at that time, Sima Yi received several honors and appointments that Cao Shuang had been given by Cao Rui shortly before the late emperor's death.  These included possession of the Plenipotentiary Tally and ceremonial Yellow Axe.  Sima Yi was also made Director of Military Affairs and Intendant of the Affairs of the Masters of Writing [lu shangshu shi]. 
Initially, this appeared to be a harmonious partnership. Because of Sima Yi's age, rank, and experience, Cao Shuang treated him like a father, consulting him on every matter and not taking action without Sima Yi's approval.  However, Cao Shuang fell in with untrustworthy advisers. Several years prior, in 230, a group of self-proclaimed scholars began to call themselves names such as the “Four Sagacious Ones”, “The Eight Intelligent Ones” and “The Three Candidates”. Cao Rui had disliked this group, and on the advice of Dong Zhao, who considered them an insult to scholarship, dismissed them all from office.  Because they were his friends, Cao Shuang appointed them to official positions.  They plotted against Sima Yi and advised Cao Shuang to ensure that all of the power was in his hands. One of them suggested that Sima Yi be promoted to Grand Tutor [taifu], which would technically remove him from most affairs of state. Cao Shuang agreed.  Shortly thereafter, Sima Yi was made Grand Tutor [taifu].  However, the edict promoting him to the position also specified that he would retain control of the army and maintain the Plenipotentiary Tally. 
After this, Cao Shuang tried to monopolize power. He appointed his brothers to high positions , appointed friends  of his as Masters of Writing [shangshu], and also appointed Li Sheng as Intendant of Henan  and Bi Gui as Colonel Director of Retainers [sili xiaowei] , granting Cao Shuang's faction enormous influence.  These men abused their authority, promoting those who agreed with them and demoting or dismissing those who disagreed.  They dismissed officials they personally disliked for trivial offenses. 
However, Cao shuang's power was not as secure as it appeared. The primary goal of promoting Sima Yi to Grand Tutor was to remove his position as Intendant of the Affairs of the Masters of Writing, thereby making Cao Shuang the one with control over the Masters of Writing. Around this time, Sima Yi met a man by the name of Deng Ai. Though originally a minor secretary in the office of a local administrator, Deng Ai had met Sima Yi when Deng came to the capital to present some accounting records. Sima Yi was astounded by his abilities and immediately transferred Deng Ai into his service. By 242, Deng Ai was appointed Prefect of the Masters of Writing [shangshu lang].  This effectively allowed him to replace Sima Yi as overseer of the Masters of Writing, with the result that Sima Yi was still able to supervise the edicts and memorials.
Additionally, Man Chong, [who had served Cao Cao since 196] who had been serving as Grand Commandant , died in 242. The position was given to Sima Yi's old associate Jiang Ji.  Through the careful appointment of a few talented individuals in key positions, Sima Yi was able to maintain his authority in the government even while he allowed Cao Shuang to remove him from a formal position of authority. The result was that Cao Shuang believed himself to dominate affairs, while his power was nowhere near as secure as it seemed.
As the inner court began to crumble under Cao Shuang, Wei's old enemies looked to take advantage of the situation. In 241, Sun Quan began a major invasion of Wei. He sent his general Quan Cong to attack Huainan. He conquered the area and destroyed the dam at Shaopo. Meanwhile, Zhuge Ke attacked Liu'an, Zhu Ran attacked Fan City, and Zhuge Jin captured Zuzhong.  Wang Ling and Sun Li counterattacked Quan Zong and drove him away.  Hu Zhi, the Wei Inspector of Jing Province, mobilized a light force and rode to aid in the defense of Fan city.  Fearing that Fan was still in danger, Sima Yi personally led an army to relieve the defenders at Fan.  Sima Yi sent an elite force over the city walls to aid the defenders.  Hearing that Fan was reinforced and that Sima Yi would soon attack him, Zhu Ran fled. Sima Yi pursued his army to Sanzhoukou, where he took many captives. After that, Sima Yi returned to the capital. 
A few months after Sima Yi's victory over Sun Quan, the court considered starting agricultural projects in Yang and Yu provinces. Sima Yi sent Deng Ai to survey the land, and Deng Ai organized a series of canals to irrigate the land. Sima Yi put Deng Ai's suggestions into practice and they eliminated not only food shortages but also local flooding problems. 
In 243, Zhuge Ke sent out spies and plotted to attack Shouchun. Sima Yi learned of this and personally led an army to Shu Commandery  and intended to attack Zhuge Ke. Sun Quan decided not to risk the confrontation, so he transferred Zhuge Ke to Chaisang. 
The following year, in 244, Cao Shuang's supporters urged him to invade Shu in order to make a reputation for himself as a strong military commander. He appointed his cousin, Xiahou Xuan, as commander-in-chief of the armies in Yong and Liang provinces. Sima Yi warned Cao Shuang that his campaign would be fruitless but Cao Shuang would not listen. 
Cao Shuang advanced into Liu Shan's territory, but the defenders fortified their position and Cao Shuang could not advance. Transportation proved to be a nightmare and food shortages devastated the local population and foreign tribes.  Sima Yi sent letters to Xiahou Xuan explaining why he should retreat. Eventually, Xiahou Xuan listened to Sima Yi's warnings and urged Cao Shuang to retreat.  In June or July of 244, Cao Shuang retreated without gaining any territory. 
An incident that widened the gulf between Cao Shuang and Sima Yi allegedly took place three years later, in 247. According to the Book of Jin, Cao Shuang moved Empress Dowager Guo to the Yongning Palace in order to keep her out of state affairs. The Empress Dowager held considerable power with the emperor being so young, and it is possible that Cao Shuang feared that she would be a rival to him and took this action to eliminate her as a threat. Supposedly, the removal of the Empress Dowager put Cao Shuang on even worse terms with Sima Yi.  However, the historian Hu Sanxing notes that the Sanguozhi frequently uses the term “the Yongning Palace” to refer to various Empresses Dowager. Hu suggests that Cao Shuang did nothing improper and that this incident was exaggerated or invented to further demonize Cao Shuang. 
We are told further that in the fifth month of 247 [June 20 – July 19] Sima Yi feigned illness and did not participate in affairs of state.  It is worth noting that, at this time, Sima Yi's wife passed away. There is no specific reason to assume that he was faking his illness, so it seems more reasonable to assume that he was distraught at the death of his wife. It is also worth noting that, at this point, Sima Yi was 68 years old and could very well have been suffering from a variety of health problems. Regardless of the reason, it was at this time that Sima Yi withdrew from court life.
In 247, Cao Shuang's old associate, Sun Li, was made Governor of Ji Province. At that time, two of the imperial relatives [the Prince of Qinghe and Prince of Pingyuan] were arguing over their territories. Sun Li consulted with Sima Yi on the matter and they decided to consult the map of Ji Province from the year when the Prince of Pingyuan gained his enfeoffment.  Sun Li determined that the district in question belonged to the Prince of Pingyuan. However, Cao Shuang favored the Prince of Qinghe and decided that the map was not to be mentioned.  Sun Li argued with Cao Shuang, so he was banished for five years.  Sun Li remained in the home of a commoner for one year. During this time, the Xiongnu and Xianbei were making frequent raids on the border, so Sun Li was appointed Inspector of Bing Province.  Before leaving to take up office in Bing, Sun Li went to speak with Sima Yi again. Sun Li expressed his dissatisfaction with Cao Shuang. Sima Yi urged him to endure the current situation and implied that a change would come soon. 
Shortly after the discussion with Sun Li, Cao Shuang transferred his partisan Li Sheng to be Governor of Jing. Before he left the capital, he went to visit Sima Yi. Accounts on what actually transpired vary. According to one source , Li Sheng simply visited Sima Yi to say goodbye before he went to his distant post. A second source  elaborates that when Li Sheng visited him, Sima Yi feigned severe illness and pretended to be enfeebled. Li Sheng did not see through the ruse and advised Cao Shuang that Sima Yi was no threat to anyone. A third source gives a very detailed account that is most likely entirely fictional.  The third story involved Sima Yi spilling food on his clothing, expressing a loss of memory, and confusing his words. This version of events is the inspiration for several famous scenes in fictional works related to the time period, and is likely just as fictional.
While it is certainly possible that Sima Yi was faking an illness, it seems more likely that, being now 69 years old, he was legitimately ill. Likewise, the death of his wife was still relatively recent, and it is quite reasonable to believe that he was still distraught by this loss.
While the exact details of the meeting between Li Sheng and Sima Yi vary wildly, it seems clear that the two met and that Li Sheng was convinced, for whatever reason, that Sima Yi would not interfere with any of Cao Shuang's future plans. 
On February 5, 249, Cao Shuang and his brothers took Cao Fang to visit Cao Rui's tomb at the Gaoping Mausoleum.  With an edict from the Empress Dowager to justify his actions, Sima Yi took command of the army at Luoyang. He closed the city gates and seized the military provisions. Then he occupied the bridge over the Luo River.  Sima Yi sent two trusted associates, Gao Rou and Wang Guan, to occupy the headquarters of Cao Shuang and his brother, Cao Xi.  Sima Yi then wrote a memorial to be sent to Cao Fang:
“When I returned from Liaodong some time ago, the late Emperor [Cao Rui] ordered Your Majesty, the Prince of Qin, and myself to mount the imperial couch, and holding my arm he expressed his deep concern on behalf of his successor. I said, ‘Both Cao Cao and Cao Pi entrusted me with their respective successors, as Your Majesty witnessed in person. There shall be no cause for worry: should anything go amiss, I will observe your command though I die.’ Now, the Grand General Cao Shuang has disobeyed the testamentary charge and trampled down the laws of the land. Within his home he emulates the imperial dignity, without he abuses power. He has destroyed the barracks and taken possession of the entire palace bodyguard, appointed his intimates to various important offices and replaced the palace guards with his own men. He has fostered corruption, indulging daily in his wantonness. Thus is his conduct outside the palace. Then, he has appointed as [dujiang] the eunuch Zhang Dang, who monopolizes important connections. He spies on [Your Majesty’s August Person], on the lookout to usurp the throne. He brings estrangement between the two palaces [that is, between Cao Fang and the Empress Dowager], wounding the relationships of blood. The empire is disturbed and the people sense danger. Your Majesty sits on the throne as a mere tolerated guest; how long can you remain in peace? This is not what the late Emperor intended when he ordered Your Majesty and me to mount the imperial couch.
Old and decrepit though I am, I dare not forget his words. Of old, Zhao Gao reveled in his desires and the Qin perished thereby; after the Lu and Huo were extirpated in good time, the lineage of the Han was perpetuated. This is a great warning for Your Majesty, and one which obliges me to act accordingly. The Grand Commandant Jiang Ji, the Prefect of the Masters of Writing Sima Fu, and others all believe that Cao Shuang has a heart which knows no Sovereign, and that he and his younger brothers therefore should not command the imperial bodyguards. I have memorialized the Yongning Palace, and the Empress Dowager has commanded me to act as I proposed in my memorial. Thereupon I ordered the official in charge, as well as the Prefect of the Yellow Gates, that Cao Shuang, Cao Xi and Cao Xun are relieved of their command of the troops and are to proceed to their fiefs as Lords, and are not to tarry to detain the imperial carriage; should they detain it or themselves linger, they will be tried and punished in accordance with military regulations. Struggling against my ailments, I have led out the army and stationed it on the pontoon bridge over the Luo River in anticipation of any eventuality.”
Cao Shuang intercepted Sima Yi's memorial before it reached Cao Fang and was uncertain what to do with it.  Xu Yun and Chen Tai went to Cao Shuang and urged him to plead guilty to Sima Yi's accusations. Yin Damun also went to Cao Shuang and assured him that he would not be harmed if he surrendered.  Furthermore, Jiang Ji sent a letter to Cao Shuang stating that no harm would come to him.  Cao Shuang believed these things and so disbanded his army, surrendering to Sima Yi. Cao Shuang was brought back to Luoyang and watched carefully at all times. 
Four days later, on February 9th, a memorial reached the throne accusing Zhang Dang [one of Cao Shuang's partisans] of having given Cao Shuang women he selected from among the palace ladies, and illicit relations were suspected. Zhang Dang was arrested and questioned. Zhang Dang alleged that Cao Shuang and the other members of his faction had been plotting against Cao Fang. Following this, Cao Shuang's party was charged with treason. All of the members were executed, as well as extended family members, including children.  Whether these accusations were true can never be known. Perhaps Sima Yi was simply inventing an excuse to purge Cao Fang's party. Perhaps Zhang Dang invented the entire story in hopes of buying himself pardon. It might even have been true.
In contrast to his harsh treatment towards the leaders of Cao Shuang's party and their families, Sima Yi was merciful towards those who served Cao Shuang but did not lead his faction, pardoning most of them, even those who had opposed his maneuver in the capital. 
Following these events, a certain woman ran into family trouble. Her name was Xiahou Lingnu and she once married to Cao Shuang's cousin. Because her husband died when she was young and childless, her family insisted that she remarry. Sima Yi learned of this and granted her special permission to adopt an heir so that the family line would continue and her family would stop troubling her.  This story originally comes from a book by Huangfu Mi called Tales of Great Women [lienü zhuan]. It is a disturbing work that often encourages insane and dangerous behavior to enforce psychotic and misogynistic social rules. One story praises a woman for burning to death rather than leave her home without a man to escort her. In this work, the story of Xiahou Lingnu states that the woman mutilated her face repeatedly to discourage suitors. Assuming there is some historical value to this tale, we can disregard the accounts of self-mutilation and instead read the story as presented above: her family wanted her to remarry and she did not wish to do. To settle the matter, Sima Yi allowed her to adopt an heir.
With Cao Shuang now dead, many wanted Sima Yi to take more formal power. An edict came appointing him Chancellor [chengxiang] and offering him the Nine Awards, but Sima Yi declined. 
The general Wang Ling and his nephew, Linghu Yu, plotted to establish Cao Biao  as a rival to Cao Fang, hoping to establish Xuchang as a new capital. Wang Ling attempted to enlist the support of his son, Wang Guang, but the younger Wang refused to oppose Sima Yi.  Nothing came of Wang Ling's conspiracy for some time.
Following the death of Jiang Ji, Sima Yi appointed Wang Ling as Grand Commandant.
In 251, Wang Ling learned that some of the Sun faction soldiers were damming the waters of the Tu River and wanted to use this as an excuse to mobilize his troops to overthrow Cao Fang and establish Cao Biao. Wang Ling began to move his soldiers, and requested permission to attack the Sun soldiers. Receiving no response from Cao Fang, Wang Ling sent his general Yang Hong to the Inspector of Yan Province, Huang Hua, to enlist his aid. Huang Hua and Yang Hong reported all of this to Sima Yi. Sima Yi mobilized the central army and marched against Wang Ling. First, Sima Yi put Wang Ling's mind at ease by issuing a pardon for his betrayal; he then sent a letter to Wang Ling criticizing Wang's actions. Realizing that he would be defeated easily if he fought Sima Yi, Wang Ling sent an officer inform Sima Yi of his decision to surrender. Wang Ling had himself tied up and brought to Sima Yi. Sima Yi released his bonds.  With six hundred soldiers as an escort, Wang Ling was sent to the capital.  However, along the way, Wang Ling died by poison.  According to most sources, Wang Ling's death was a suicide, but the timing is highly suspect, especially considering that after Wang Ling surrendered, Sima Yi executed many officials who were involved with his plot, as well as their families.  Of Wang Ling's family, only his sister was spared.  Cao Biao was also executed. 
On September 7, 251, Sima Yi passed away.  He was 72 years old.
Sima Yi's sons, Sima Shi and Sima Zhao, gained authority after their father's death. After a series of political struggles and military conquests, they established a position of unassailable authority within Wei. After the death of Sima Zhao, Sima Yan – the grandson of Sima Yi – formally dethroned the last Wei emperor and founded the Jin Dynasty, which finally unified China. When Sima Zhao became King of Jin, Sima Yi was given the posthumous title King Xuan of Jin. When Sima Yan officially took the throne, Sima Yi was promoted to Emperor Xuan and given the temple name Gaozu.
1 ZZTJ Jian'an 13, J
2 Cui Yan was once an official under Yuan Shao. Later, under Cao Cao, he became the head of the Department of the East and the Department of the West. These departments were responsible for recommending and promoting officials in the civil and military administrations. As such, Cui Yan's praise was very much worth considering. [ZZTJ Jian'an 13, J; also de Crespigny, ZZTJ Jian'an 13, note 14]
3 ZZTJ Jian'an 13, L
4 The story told by ZZTJ [Jian'an 13, L] says the following: “Sima Yi sought to excuse himself on the grounds that he had rheumatism. Cao Cao was angry and was going to have him arrested. Sima Yi was frightened and took the post. As de Crespigny says in his note on that passage [Jian'an 13; note 17], “There is thus a certain irony in the story that he [Sima Yi] had to be dragooned by Cao Cao into service, and it may be to good to be true.”
5 The Master of Records served as a secretary to a military commander, in this case Cao Cao. Though it only came with a rank/salary of 600 shi, an officer in this position had access to extremely sensitive and vital information, making it an extraordinarily important position. [de Crespigny, Later Han Military Organisation]
6 ZZTJ Jian'an 20, I [in which he is described as such]
7 ZZTJ Jian'an 20, I
8 A Major in the army served as the second-in-command of the general who controlled it. As Major to the Army of the Chancellor, Sima Yi served as Cao Cao's second-in-command. [de Crespigny, Later Han Military Organisation]
9 ZZTJ Jian'an 24, P
10 ZZTJ Jian'an 24, U
11 ZZTJ Jian'an 24, TT
12 ZZTJ Huangchu 5, 9 gives Sima Yi's rank at this time as shangshu puyi. During the Han [and presumably Wei] the “shangshu” were the Masters of Writing, in charge of [among other things] drafting edicts from the emperor, so they took their instructions directly from the highest level of government. Regarding the designation of Sima Yi as shangshu puyi, it is unclear what the addition signifies. From my own extrapolation, there was a Supervisor of Internuncios [yezhe puye] under the Minister of the Household. Though the Prefect of the Masters of Writing was designated as shangshu ling, it is possible that Sima Yi served in some supervisory role in this body and that his rank should be written as shangshu puye or that that of the Supervisor of Internuncios should be written yezhe puyi. Due to inadequate resources, I cannot currently investigate this matter further. The previous discussion should not obscure the fact that Sima Yi was, in 244, one of the Masters of Writing and held some special position within that role.
13 ZZTJ Huangchu 5, 9
14 ZZTJ Huangchu 6, 1
15 ZZTJ Huangchu 7, 12 – this passage also mentions Cao Xiu, but that is unsupported by the biographies of the parties involved [those of Chen Qun, Cao Zhen, and Sima Yi only mention those three and Cao Xiu's does not mention the incident].
16 During the time of Emperor Ling, the position of General of the Agile Cavalry was an honorific one that did not come with an actual field command. It was a very high honor, just below that of Grand General [who ranked above the Three Excellencies and was thus second only to the emperor]. It is unknown whether this title inherently included field command under Cao Rui, but it is clear from context that it was still, if nothing else, a very great honor. [de Crespigny, Later Han Military Organisation]
17 ZZTJ Huangchu 7, 23; see also Fang, note 23, regarding the same passage
18 ZZTJ Huangchu 7, 27
19 ZZTJ Taihe 1, 10
20 ZZTJ Huangchu 1, 27
21 Shen Yi and Meng Da had a complicated history. Shen Yi's brother, Shen Dan, was once Grand Administrator of Shangyong. He was defeated by an army led by Meng Da and Liu Feng, at which point Shen Dan and Shen Yi joined Liu Bei. Meng Da later defected to Wei. Shen Yi led a revolt in Yi but was defeated and fled to Wei as well. ZZTJ summarizes this by saying that they were “at odds”.
22 ZZTJ Taihe 1, 14
23 Paraphrased in Fang, note 14.6 of ZZTJ Taihe 1, 14
24 ZZTJ Taihe 1, 15 - I rephrased part of Sima Yi's letter to Meng Da for clarity.The passage "[The men of Shu, both wise and foolish], all have been..." originally read ""The Shu, regardless of wise and stupid, all have been..."
25 ZZTJ Taihe 2, 1
26 ZZTJ Taine 2, 2
27 ZZTJ Taihe 2, 24
28 ZZTJ Taihe 2, 29
29 ZZTJ Taihe 2, 31
30 ZZTJ Taihe 2, 5
31 ZZTJ Taihe 2, 7
32 ZZTJ Taihe 2, 11
33 ZZTJ Taihe 2, 15
34 ZZTJ Taihe 2, 19
35 ZZTJ Taihe 2, 36
36 ZZTJ Taihe 3, 1
37 ZZTJ Taihe 4, 8
38 ZZTJ Taihe 4, 13
39 ZZTJ Taihe 4, 16
40 ZZTJ Taihe 5, 4
41 ZZTJ Taihe 5, 5 – this passage comes from Xi Zuochi's Chronicles of Han and Jin.
42 According to Fang's notes, [Taihe 5 and 8] the information in ZZTJ regarding this campaign is from the Chronicles of Han and Jin [Han Jin Chunqiu] by Xi Zuochi [who also wrote the Records of Xiangyang [Xiangyang Ji]. Xi was an unapologetic supporter of the state of Shu and was among the first to argue that Liu Bei's state was the legitimate successor to the Han - as is evidenced by the fact that he refers to Liu Bei's state as Han rather than Shu. Xi Zuochi is well known for being extremely biased in favor of the Liu faction. As such, any information from the Chronicles of Han and Jin [and Records of Xiangyang] must be regarded with deep skepticism and should be considered generally unreliable.
43 ZZTJ Taihe 5, 8 – this passage comes from Xi Zuochi's Chronicles of Han and Jin.
44 Guo Huai's Sanguozhi biography
45 ZZTJ Taihe 5, 8 - Xi Zuochi's work mentions that Zhuge Liang's forces defeated 3,000 Wei soldiers and somehow captured 5,000 sets of armor and 3,100 crossbows from them – one should not need to point out the logical contradiction in these numbers.
46 ZZTJ Taihe 5, 9
47 ZZTJ Qinglong 2, 1
48 ZZTJ Qinglong 2, 7
49 ZZTJ Qinglong 2, 8
50 ZZTJ Qinlong 2, 9
51 ZZTJ Qinglong 2, 10
52 ZZTJ Qinglong 2, 13
53 ZZTJ Qinglong 2, 14 and Qinglong 2, 15
54 ZZTJ Qinglong 2, 18
55 ZZTJ Qinglong 2, 23; this passage is divided into paragraphs A, B and C, which are all derived from different sources with varying degrees of reliability.
56 ZZTJ Qinglong 2, 23. Paragraph A of this passage is taken from the Sanguozhi biography of Cao Rui and seems reliable. It simply states that Zhuge Liang and Sima Yi did not fight each other.
57 Paragraph B of Qinglong 2, 23 says that this story is from the Chronicles of Wei [Wei Shi Chunqiu], which was written by Sun Sheng. Sun Sheng wrote many comments on the Sanguozhi, often providing harsh moral criticisms of the individuals involved. He is known for providing embellishment [in Jingchu 3, 4 he states that Cao Rui's hair was so long it reached the ground when he was standing] and his information is of limited reliability. As such, I am personally disinclined to view incidents such as this as dramatic embellishments.
58 Paragraph C of Qinglong 2, 23 [the source of this information] comes from the Chronicles of Han and Jin [Han Jin Chunqiu], a work by Xi Zuochi – the accuracy of which I discussed previously in note 42. There does seem to be a degree of reliable support for this passage, however. It is recorded in Xin Pi's Sanguozhi biography that he was appointed as a military adviser and sent with great authority to oversee Sima Yi's actions.
59 Zhuge Liang's analysis of Sima Yi seems correct, given his actions regarding Meng Da in 220, when he attacked Xicheng without permission from the court. It seems likely that Sima Yi was indeed acting on his own initiative and would attack or defend as he saw fit.
60 The purpose of this envoy is not stated, though given the context, it seems likely that it was to offer battle to Sima Yi or to present him with the [likely fictional] bonnet and clothing mentioned above.
61 ZZTJ Qinglong 2, 24; this passage is from Sun Sheng's Chronicles of Wei [Wei Shi Chunqiu] and is almost certainly dramatic embellishment. While it is tempting to attribute such prescience to a man with Sima Yi's reputation, and while he may have had other reasons for suspecting that Zhuge Liang was in poor health [spies in the camp, information from locals, or so on], the story about him gleaning the information from an envoy who did not know this himself seems too dramatic to be true.
62 ZZTJ Qinglong 2, 26
63 ZZTJ Qinglong 2, 27. This account is also from the Chronicles of Han and Jin, which – as I have noted before – is very biased in favor of the Liu faction and is notoriously unreliable [see notes 42 and 58]. This is the source of the popular folk story involving Sima Yi fleeing from a statue of Zhuge Liang. The passage concludes with, "The people made it a saying, 'Dead Zhuge has put live Zhongda to flight!' When he heard this Sima Yi laughed and said, 'It is because I can take the measure of the living, but not of the dead.'" Given the source, this seems complete fiction.
64 Wei Yan's Sanguozhi biography
65 ZZTJ Qinglong 3, 1; I am not certain of the translation of taiyu. De Crespigny [in Later Han Civil Administration] gives the position of Grand Commandant as taiwei rather than taiyu. Fang refers to several other officials as taiyu at various times, including Yang Biao, Gao Rou, Man Chong, and Jiang Ji. Yang Biao once served as taiwei [according to de Crespigny, ZZTJ Jian'an 1, Y] of the Han. The position of Grand Commandant [taiwei] was abolished by Cao Cao in 208. It seems that the position of taiyu appeared during the reign of Cao Pi or Cao Rui, replacing the now-defunct taiwei. As such, I have chosen to translate the rank of taiyu as Grand Commandant.
The Grand Commandant [taiwei] was one of the Three Excellencies – technically the highest of the three. During the time of the Han Dynasty, the position was only irregularly filled. The position of taiyu seems to have been filled regularly under Cao Rui.
66 ZZTJ Chuping 1, Y
67 ZZTJ Chuping 2, KK
68 ZZTJ Jian'an 9, O
69 ZZTJ Jian'an 12, F
70 ZZTJ Taihe 2, 41
71 ZZTJ Taihe 6, 5
72 ZZTJ Taihe 6, 11
73 ZZTJ Qinglong 1, 3
74 ZZTJ Jingchu 1,12
75 ZZTJ Jingchu 1, 13
76 ZZTJ Jingchu 2, 1
77 ZZTJ Taihe 2, 41
78 ZZTJ Jingchu 2, 3
79 ZZTJ Jingchu 2, 12
80 ZZTJ Jingchu 2, 13
81 ZZTJ Jingchu 2, 14
82 ZZTJ Jingchu 2, 15; It is important to view the execution of Zhang Jing in context. Sima Yi was leading a relatively small [about 40,000 soldiers] army that was isolated in enemy territory [Liaodong was far from the capital and it would be impossible to secure additional supplies or soldiers due to the geography of the region] and experiencing harsh conditions [a month of rain]. In such situations, Sima Yi must have been concerned with mutiny and desertion. Therefore he could not allow one of his officers to violate his orders.
83 ZZTJ Jingchu 2, 15; Sima Yi's discussion on the subject is given as a direct quote, and so the details and authenticity of it are of questionable reliability. However, it is most likely a faithful representation of Sima Yi's logic and planning, even if the specifics of the discussion are not.
84 ZZTJ Jingchu 2, 17
85 ZZTJ Jingchu 2, 18
86 ZZTJ Jingchu 2, 19; it is during this exchange that Sima Yi is said to have made his famous speech about the five options of an army. It is as follows: "The essential points in war are five. If you can fight, then fight; if you cannot fight, then defend yourself; if you cannot defend yourself, then flee. The remaining two points are nothing else than surrender and death.” Because this is stated as a direct quote it is questionable whether Sima Yi actually said this or not, though there is no specific reason to doubt it.
87 ZZTJ Jingchu 2, 20
88 ZZTJ Jingchu 2, 21
89 ZZTJ Jingchu 2, 22
90 In 226, when Cao Pi was ill, he appointed Cao Zhen, Sima Yi, and Chen Qun to serve as guardians and guides for Cao Rui [ZZTJ Huangchu 7, 12]. Cao Rui intended to do the same for his heir.
91 Fang, note 41.4 of ZZTJ Jingchu 2, 41
92 ZZTJ Jingchu 2, 41
93 ZZTJ Jingchu 2,42; the basic text only mentions Xiahou Xian and Cao Zhao. Fang's note 42.2 on the passage says that Liu Fang and Sun Zi were disliked by Xiahou Xian, Cao Zhao, and Qin Lang. As Qin Lang was estranged along with Xiahou Xian and Cao Zhao, this seems to be true.
94 ZZTJ Jingchu 2, 43
95 ZZTJ Jingchu 2, 44
96 ZZTJ Jingchu 2, 46
97 ZZTJ Jingchu 2, 47
98 Having recently completed his campaign against Gongsun Yuan, Sima Yi was on his way home.
99 ZZTJ Jingchu 2, 48
100 ZZTJ Jingchu 3, 1
101 ZZTJ Jingchu 3, 5
102 Cao Fang's Sanguozhi biography
103 This suggestion is found in the Chronicles of Wei [Wei Shi Chunqiu] by Sun Sheng, who is prone to dramatic embellishments. As such, it should be viewed with skepticism.
104 Cao Kai was the son of Cao Zhang. Cao Zhang was the son of Cao Cao and Lady Bian, making him Cao Pi's full brother. Thus, Cao Kai was Cao Rui's cousin. This would make Cao Fang the nephew of Cao Rui.
105 ZZTJ Jingchu 3, 5
106 The main text of ZZTJ Jingchu 3, 5 reads as though Cao Shuang and Sima Yi received all of these honors at the same time. Fang states in note 5.2 of Jingchu 3, 5 that Cao Shuang's Sanguozhi biography explains that he received these honors from Cao Rui. Cao Shuang and Sima Yi only received the appointment of chizhong at the same time.
107 Both of these carried the symbolic authority of the emperor, granting various privileges to those who held them, including the authority to execute officials without prior approval.
108 ZZTJ Jingchu 3, 5; see also Fang's note 5.2 on the subject. According to de Crespigny: Later Han Civil Administration, this appointment gave an official the authority to oversee the affairs of the Masters of Writing, allowing them to view all of the edicts and memorials that passed through the palace.
109 ZZTJ Jingchu 3, 6 [from the sanguozhi biography of Cao Shuang]
110 ZZTJ Taihe 4, [passages 2, 3, and 4]
111 ZZTJ Jingchu 3, 7
112 ZZTJ Jingchu 3, 8
113 ZZTJ Jingchu 3, 9
114 Fang's note 9 of Jingchu 3, 9
115 ZZTJ Jingchu 3, 10
116 Those friends being Deng Yang, Ding Mi, and He Yan, with He Yan in charge of selecting officials.
117 The Intendant of Henan was in charge of the capital commandery, making him a Grand Administrator with increased authority.
118 The Colonel Director of Retainers was in charge of the capital province [that is, Si Li], making him a Governor or Inspector with greater power. In addition to the usual supervisory powers, he could impeach/investigate central government officials.
119 ZZTJ Jingchu 3, 12; all of these men were of the group that Cao Rui exiled from government in 230.
120 ZZTJ Jingchu 3, 13
121 ZZTJ Jingchu 3, 14 cites the example of Fu Jia. Passage 15 cites a similar case with Lu Yu, who had been demoted to make room for He Yan. Passage 16 presents another example: Cao Shuang's Chief Clerk, Sun Li [who had been given the position by Cao Rui to supervise Cao Shuang] was sent away to be Inspector of Yang Province.
122 ZZTJ Zhengshi 2, 10 gives Deng Ai's rank as such, the Prefect of the Masters of Writing.
123 ZZTJ Jingchu 3, 17
124 ZZTJ Zhengshi 3, 4
125 ZZTJ Zhengshi 2, 2
126 ZZTJ Zhengshi 2, 3
127 ZZTJ Zhengshi 2, 4
128 ZZTJ Zhengshi 2, 6; note that while Sima Yi was now Grand Tutor, he had been allowed to keep control over military affairs, presumably so that he could easily assist in just this sort of situation.
129 Fang, note 7.1 of Zhengshi 2, 7
130 ZZTJ Zhengshi 2, 7
131 ZZTJ Zhengshi 2, 10
132 Shouchun was located in Shu commandery.
133 ZZTJ Zhengshi 4, 8. According to the text of ZZTJ [taken from Zhuge Ke's Sanguozhi biography], Sun Quan decided against the confrontation because a magician warned him not to. While it is possible – given some of his past decisions - that Sun Quan would accept the words of a self-proclaimed mystic regarding military affairs, it seems more likely that he recalled his defeat in 241 and did not want to risk greater damage by fighting an army personally commanded by Sima Yi.
134 ZZTJ Zhengshi 5, 2
135 ZZTJ Zhengshi 5, 7
136 ZZTJ Zhengshi 5, 9
137 ZZTJ Zhengshi 5, 10
138 ZZTJ Zhengshi 8, 6
139 Fang, note 6.1 of Zhengshi 8
140 ZZTJ Zhengshi 8, 6
141 Fang's note 9.1 of Zhengshi 9, 9. Taken from Sun Li's Sanguozhi biography.
142 Fang's note 9.2 of Zhengshi 9, 9
143 ZZTJ Zhenghi 9, 9
144 Fang's note 9.5 of Zhengshi 9, 9
145 ZZTJ Zhengshi 9, 9
146 The Book of Jin biography of Sima Yi
147 Cao Shuang's Sanguozhi biography
148 That source is the Records of the End of Wei [Wei Mo Zhuan]. The author of this work is unknown, so the reliability of the work cannot be verified. An adapted form of this story appears in ZZTJ Zhengshi 9, 10.
149 ZZTJ Zhengshi 9, 10
150 ZZTJ Jiaping 1, 1
151 ZZTJ Jiaping 1, 2
152 ZZTJ Jiaping 1, 3
153 ZZT Jiaping 1, 4
154 ZZTJ Jiaping 1, 6; ZZTJ says that Sima Yi sent them, but this is somewhat inconsistent with the account in various Sanguozhi biographies.
155 ZZT Jiaping 1, 26
156 ZZTJ Jiaping 1, 10
157 ZZTJ Jiaping 1, 11
158 ZZTJ Jiaping 1, 12
159 ZZTJ Jiaping 1, 15
160 ZZT Jiaping 1, 21
161 Cao Biao was the Prince of Chu and a son of Cao Cao.
162 ZZTJ Jiaping 1, 29
163 Fang's note 29.2 of Jiaping 1, 29
164 ZZTJ Jiaping 3, 5
165 ZZTJ Jiaping 3, 6
166 ZZTJ Jiaping 3, 7
167 ZZTJ Jiaping 3, 8
168 Guo Huai's Sanguozhi biography. Wang Ling's sister was Guo Huai's wife.
169 ZZTJ Jiaping 3, 14
170 ZZTJ Jiaping 3, 17
Last edited by capnnerefir
on Mon Mar 25, 2013 3:47 pm, edited 2 times in total.