Seongho Yi Ik’s New Approach to Zhijue 知覺 and Weifa 未發: Stimulation by Western Learning and the Expansion of Confucianism

Abstract

This paper explores the 18th-century Joseon Confucian scholar Seongho 星湖 Yi Ik’s 李瀷 (1681~1763) theory on philosophical anthropology in the context of Confucianism through his theory of the heart-mind 心論. This study begins by examining which intellectual heritage he innovated, what intellectual resources he used in the process, and how his theories diverged from those of other Joseon Confucian scholars. Through Western learning books, Seongho obtained the rational soul theory and anatomical and physiological knowledge about the brain, based on which he reinterpreted the controversial Neo-Confucian concepts of zhijue 知覺, and the Weifa-Yifa theories 未發已發論. He acknowledged the primacy of the brain, which differs from the general principles of Neo-Confucianism. Seongho did not imbue zhijue itself with moral meaning, but considered the whole process of perception–recognition–judgment as the weifa state. At this point, yifa is determined by whether moral judgments are made. If yifa is the moment of moral judgment, the relationship between weifa and yifa must be regarded as the relationship between the operation of physical perception–cognition and rational judgment–moral practice. In Seongho’s perspective, moral practice is not a process of static cultivation, but the result of active moral determination.

1. Introduction

The 18th-century Joseon Confucian scholar Yi Ik 李瀷 (pen name Seongho 星湖; 1681~1763; hereafter Seongho) is a figure whose reputation is relatively unknown despite his contribution to the Confucianism of late Joseon. He was a critical scholar of Confucianism who, by the character and originality of his thought, is historically representative of the Confucianism distinctive of the later period of Joseon’s philosophical history. Seongho passed on the philosophical legacy he inherited from the previous generation after developing it through his own unique methods. Seongho’s philosophy lies between that of Yi Hwang 李滉 (pen name Toegye 退溪; 1501–1570; hereafter Toegye), representing Joseon Confucianism, and that of Jeong Yakyong 丁若鏞 (pen name Dasan 茶山; 1762–1836; hereafter Dasan), who represents Silhak 實學 or Practical Learning, a new academic field that appeared in the late Joseon Dynasty. The significance of Seongho’s philosophy and position are complex because it succeeded in the tradition of Joseon Confucianism while changing and developing it in a new and innovative way.

Politically, Seongho belonged to the Kiho Southern 畿湖南人 faction based in the capital area. The Seongho School 星湖學派 was the most active of the Kiho Southerners. Seongho was born while his father was in exile due to factional strife, and after the death of his father, he moved to his mother’s hometown of Ansan 安山 in Gyeonggi 京畿 Province, where he grew to become one of the Southern faction’s central figures.1

Due to the factional strife of the time, Seongho and his brothers were unable to hold official governmental positions since the political status of the Southerners was weakened by the Old Doctrine 老論 (K. Noron), a rival political faction. Instead of participating in politics, he deepened his study of Confucianism by teaching and discussing it with his disciples. Seongho held high respect for Toegye in particular, who was called the leader of Confucianism in Joseon, and tried to expand upon Toegye’s philosophy—which was based in Yeongnam 嶺南—within his own region. Additionally, Seongho acquired his academic leanings from Seohak 西學 (C. Xixue) or Western Learning, which enabled him to take his discipline in a new direction.

Western Learning refers to the theology and philosophy of Scholasticism and the natural science of the European Renaissance, which was transferred to China through translations by the Jesuits from the 16th to the 19th century. While Seongho was active, books on Western Learning were already in circulation in Joseon, and there were multi-faceted attempts by the government to adopt the Western Calendar systems revised by the Jesuits—the Shixianli 時憲曆, or Calendar of the Conformity of Time.

However, Western Learning was openly accommodated by some in Joseon only by the end of the 18th century. At the time, Confucian scholars already had a positive attitude toward the practicality of Western mathematical and astronomical knowledge, but Neo-Confucianism 性理學 (K. Seongnihak) still protected its seat as the traditional hegemon. Furthermore, the doctrine of Christianity, because of its emphasis on faith in a personified God and how one’s actions in life determined whether that person goes to Heaven or Hell after death, gave birth to intense criticism in Joseon. Since this was in opposition to the theory of li-qi 理氣論, the metaphysical foundation of Neo-Confucianism, Western Learning had the potential to cause political conflict. In this context, it is clear that his choice to research Western Learning was voluntary and proactive.2

Seongho was able to research Western Learning in a relatively free and open manner before it became the subject of widespread political conflict. His most significant assets were the books from China that his father Yi Hajin 李夏鎭 (1654–1682) had purchased and brought home after his time as an envoy in Beijing. Among those books, there were several books on Western Learning that Jesuits had translated into Chinese.3 He not only studied these books himself, but also encouraged his disciples to study them. As Seongho allowed free and open discussion, opinions about Western Learning varied among his disciples. As a result, the scholarly attitude towards Catholicism, which was the core of Western thought and learning, was divided within the Seongho school into the pro-Western Learning 親西派 versus the anti-Western Learning 攻西派 groups after Seongho’s death.

However, with time, Confucian scholars began to regard Catholicism as heresy because Catholic doctrines, such as the abolition of ancestral rites, conflicted with Confucian traditions. It was at the end of the 18th century, decades after the death of Seongho, that Western Learning became a serious political issue in Joseon. The Southerners who were associated with Western Learning were ruthlessly persecuted. During this period, the Old Doctrine faction 老論, which controlled the nation at the time, attacked their political rival, the Southerners, using Catholicism as an excuse for the political purge. This political tension drove young scholars of the Kiho Southern faction into crisis, including Yi Byeok 李蘗 (pen name Gwangam 曠庵; 1754–1786), Yi Seunghun 李承薰 (pen name Mancheon 蔓川; 1756–1801), and Dasan and his brothers.4 As a result of the political dispute caused by Christianity, Dasan, an outstanding bureaucrat recognized by King Jeong Jo 正祖 (1752–1800, r. 1776–1800), was exiled for 18 years for his research on Western Learning and was not allowed to resume a position in the government even after being released.

At that time in Joseon, Catholicism slowly began to spread, and the Old Doctrines strongly suppressed it through religious and ideological censorship using government control. In the process, anti-Catholic persecution and purges occurred several times nationwide. Several upper-level intellectuals and a considerable number of middle-and-lower class people were executed because they had converted to Christianity.5

Western Learning sealed the Southern faction’s fate, but paradoxically, the situation has reversed in modern times. This is because Seongho and Dasan’s works are often judged in accordance with the Western Learning they studied. In modern Korea, Seongho and Dasan are considered innovators who built Silhak 實學, or Practical Learning, in contrast to their time’s conservative and speculative Neo-Confucianism. In their approach to Practical Learning, they used new intellectual resources from the West to change the academic field during the late Joseon period. Furthermore, they are regarded as progressive proponents of modernization compared to other Confucian scholars of the time. However, these assessments require careful examination, because it is easy to overlook their Confucian studies’ foundation, goal, method, and strategy if the introduction of Western Learning is viewed as an indicator of modernization.

For example, the common belief of contemporary scholars in Korea was that Seongho did not accept the religious doctrine of Catholicism, but only accommodated the practical technique and ethics of Western Learning. (Geum 2003, pp. 82–83). This is because the purpose of Seongho’s approach to Western Learning was not the introduction of the West itself, nor was it the propagation of Western Learning or the substitution of Confucianism through it. His interest in Western Learning was to use it as a resource or reference for the development of Confucianism.

In this study, I would like to examine Seongho’s understanding of the human being through his “Simseol 心說 (Theory of heart-mind)”6 in Seonghojeonjip (Complete Works of Seongho Yi Ik),—which combines aspects of both orthodox Neo-Confucianism and Western Learning—to explore which intellectual heritage he innovated and how, what intellectual resources he used in the process, and how his theories diverged from those of other scholars. The starting point of Seongho’s theory of the heart-mind lies in defending Toegye’s theory against criticism from other scholars. However, his thought is innovative in that it diverges from Toegye and his contemporaries through its use of Western learning theories. In this context, Seongho’s theory of the heart-mind enables us to see both the core issues and new subject matter, the development and succession of academic tradition, and the revitalization and reorientation of Confucian philosophy in the 18th century Joseon.

2. Seongho’s Introduction of Western Learning in the Perspective of the Theory of the Heart-Mind

It is the theory of heart-mind that demonstrates Seongho’s depth and knowledge of Western Learning. Neo-Confucianism was the theoretical base of most Confucian scholars. However, not all scholars engaged with the theory of heart-mind and nature 心性論 (K. Simseongron) as debates in metaphysics and the moral philosophy of Neo-Confucianism. In his lifetime, Seongho studied various fields ranging from traditional classical learning 經學 (C. Jingxue) to various theories of nature and social reform. His diverse range of academic interests is reflected in his encyclopedic Seonghosaseol 星湖僿說, or The Collection of Essays of Seongho. Seongho explored the theory of heart-mind and nature in his writings, such as “Simseol 心說 (theory of the heart-mind),” “Jigak 知覺 (awareness/perception)”, and “Seogugui 西國醫 (Western doctor)”.

Interestingly, he uses unfamiliar western discourses to explore the theory of heart-mind, which stems from a traditional Neo-Confucian theoretical framework. In order to understand the multi-layered context of his theory of heart-mind, we first need to examine Seongho’s position on similar theories in Western studies. One of Seongho’s disciples, Shin Hudam 愼後聃 (1702–1762), once asked what the theoretical core of Western Leaning was, and Seongho answered as follows. 7

These are the brain-pouch theory 腦囊說 and the theory of three types of soul 三魂說 (According to Matteo Ricci). The brain-pouch 腦囊 (K. noenang) is the subject of memory. It is located in the head, the basic foundation that receives life. The theory of three types of soul states that there are three types of souls: the vegetative soul 生魂, possessed by plants, the sensitive soul 覺魂, possessed by animals, and the rational soul 靈魂, possessed only by humans. These two theories differ from the theories of heart-mind and the nature of Neo-Confucianism, but it cannot be asserted that they are entirely different from our theory.

(Shin 2014, pp. 41–43)

Although there are minute differences in detail, Seongho thought that the brain-pouch theory, which states that the brain is responsible for mental activities such as storing memories, and the theory of three types of soul, which divided all things into having one of three types of souls, were both correlated to the theory of heart-mind and nature. As is well known, the theory of three types of soul was one of the critical doctrines of Christianity that a Jesuit missionary, Matteo Ricci (利瑪竇, 1552~1610), and his colleagues were trying to convey to the Chinese during their mission to China. To understand God as the world’s creator, Jesuits first had to explain the mechanism and purpose of the human being created by God. They introduced the concept of the rational soul (anima rationalis; anima intellectiva), the highest of the three kinds of souls, given only to human beings. This rational soul practices moral judgment and is immortal, existing forever even after the extinction of the body. This theory states that a soul, independent from the body, must go to Heaven or Hell after the death of one’s body due to its actions in life.8

Contrary to the expectations of the Jesuits, the theory of three types of soul was not easily accepted at that time by the Confucian scholars in China and Joseon. The way of dividing all things into three classes and classifying the principle of life into three stages was unfamiliar, but not in opposition, to Confucianism.

Additionally, the fact that the uppermost soul ultimately serves an intellectual and moral function was a convincing argument for Confucian scholars. However, the most contentious point was that the soul of the human being is immortal, and that every human being must go to Heaven or Hell after death, depending on one’s behavior in life.

Both parts of the theory of Heaven and Hell were unacceptable because the former opposed the Confucian understanding of the human soul, as the human soul in Confucianism is understood as the condensation and expansion of the qi 氣 (material force or energy), and the latter resembled the Buddhist theory that Confucian scholars regarded as heresy. Seongho clearly recognized the differences between Western Leaning and Confucianism, but did not wholly exclude the theory of three types of soul in terms of the category and orientation of the theory. This is because the way of explaining human morality in the theory of three types of soul is similar to the theory of Confucianism. However, the brain-pouch theory is even more interesting.

In East Asian medicine, the brain was known to play an essential role in the maintenance and preservation of life, but was not regarded as the subject of mental activity of human beings. In the history of Confucianism, it was the function of xin 心 or the heart-mind, to control human beings by accepting, judging, and responding to external stimuli. Against this theoretical background, Seongho encountered the unfamiliar Western theories that connect the mind and body’s response to the brain.

It was through the book Zhuzhiqunzheng 主制群徵, or All Signs Indicating That the Lord Rules (1636)9, that Seongho obtained anatomical and physiological information about the brain. The Zhuzhiqunzheng is a text on natural sciences, written as an apology to prove that the purpose of all creation—such as the creatures of the sky, sea, land, and human beings—and their relationship to natural phenomena were the providence of God. Accordingly, the contents on the anatomy and physiology of the human body, including the brain, are only introduced in Section 5. This text introduces other topics of natural science, such as astronomy and meteorology, but Seongho focused only on Section 5, “Yirenshenxiangzhi 以人身向徵 (Evidence from the Human Body),” which contained information on medieval European anatomy, physiology, and medicine.

Seongho introduces and comments on this portion of the text in various works such “Jigak 知覺 (C. Zhijue, awareness/perception)”, and “Seogugui 西國醫 (C. Xiguoyi, Western doctor)”.10 Here, a question arises: why did Seongho apply knowledge from the field of natural science and not from moral philosophy or metaphysics in order to study the theory of heart-mind? Or, more specifically, why did Seongho utilize physiological–medical theory for studying the theory of heart-mind, even though the two subjects are not necessarily connected in traditional Confucianism? To address this question, we must first begin with the starting point of Seongho’s theory of heart-mind.

3. Seongho’s New Approach to the Four Beginnings and Seven Emotions

The theory of Four Beginnings and the Seven Emotions 四端七情論 (K. sadanchiljeongnon, hereafter the Four-Seven Debate) is one of the most heated topics of debate within Joseon Confucianism.11 The four beginnings四端, which appear in Mengzi 孟子, refer to four kinds of moral emotions.12 The seven emotions 七情, which appear in Liji 禮記 or the Book of Rites, refer to seven basic human emotions.13 To explain the structure and function of human beings on a metaphysical basis, Neo-Confucian scholars such as Cheng Yi 程頤 (1033–1107) and Zhu Xi 朱熹 (1130–1200), attempted to integrate the psychological, cognitive, and moral processes of human beings with the theory of li-qi through the theory of the Four-Seven.

There is a difference between moral and basic emotion, but fundamentally the Four and Seven belong to emotions and, therefore, are modes of qi. However, both the Four and Seven are also manifestations of li in that they are functions of the heart-mind 心, where nature 性 dwells. Contrary to the fact that both are actualized by li, the Four and Seven must be categorized separately. This is because the Four are moral emotions that are innately good, and the Seven are basic human emotions that can lead to both good and evil. It is due to this complexity that vastly different conclusions are drawn by Confucian scholars depending on where the theoretical focus is placed, despite using the same concepts and principles.

One of the reasons for the complexity of the Four-Seven Debate is that the heart-mind is not the ultimate subject that controls judgments. In Confucianism, mental activities such as emotion, cognition, reasoning, and judgment are functions of the heart-mind, but there exists a genuine subject that controls the mental activities on a metaphysical level and gives value orientation to the process of the heart-mind. That is nature 性 as li. In other words, through the intervention of nature, which is a metaphysical principle, the Four-Seven Debate extends beyond the scope of psychology or ethics and into the realm of metaphysical theory.

It was through the debates between Toegye and Gi Daeseung 奇大升 (pen name Gobong 高峯; 1527–1572, hereafter Gobong) that the Four-Seven Debate was officially formulated for the first time in Joseon.14 According to Toegye, who sought to elaborate on the concept of the Four and Seven, the Four originate from pure goodness and completeness itself, while the Seven are derived from qi, which can be good or bad. This is because Toegye wanted to distinguish the four beginnings’ fundamental goodness from general and basic emotions. Since this is contradictory to the traditional interpretation, a young scholar, Gobong, sent a letter to Toegye to debate this issue in depth. Toegye sought to separate the Four and Seven from the traditional interpretational framework because he wanted to emphasize the perfection and the goodness of moral emotion in the meaning and purpose of li.

In Neo-Confucianism, li had no mobility or activity because it was not related to materiality, but rather to value and ideology. However, to emphasize the goodness of the four beginnings, Toegye asserts that, in the case of the four beginnings, “li issues/arouses and qi follows li (理發而氣隨),” and with the seven emotions, “qi issues/arouse and li rides on qi (氣發而理乘).” Gobong criticized Toegye’s theory, arguing that both the four beginnings and the seven emotions are manifestations of “qi [issuing] with li riding on it.” Toegye accepted Gobong’s criticism in various ways, but he did not change the fundamental composition of his thought, and Toegye’s theory became the established theory among the Southerners. Toegye believed that by emphasizing the autonomy and activeness of li, the human being could be moral by activating the pure goodness of the Four, regardless of the environmental factors of the external world.

Toegye’s position, which emphasized the vitality of li more than traditional Neo-Confucian theories, invited various criticisms from other scholars. Eventually, this problem was transferred to the next generation. In particular, Yi I 李珥 (pen name Yulgok 栗谷; 1536–1584; hereafter Yulgok) criticized Toegye’s theory by acknowledging Gobong’s theory. His key argument is that both the Four and Seven are “qi issue/arouse 氣發”. That is why Yulgok’s theory was considered a competing theory to be disputed by the Southerners who wanted to succeed Toegye.

The Four-Seven Debate is one of the critical theories Seongho had been determined to elaborate on through his long years. He organized his position on the Four-Seven Debate in Sachilsinpyeon 四七新編 (New Transcription on the Four-Seven Debate). The first manuscript of Sachilsinpyeon was written at the age of 35, but Seongho did not complete this work because he wanted to incorporate the questions, doubts, and advice of his disciples and compile a more complete work.

Seongho wrote Sachilsinpyeon to counter Yulgok’s critique of Toegye’s theories on the Four and Seven and strengthen Toegye’s position. Conclusively, however, his theory was not restricted to the advocacy of Toegye, or criticism of Yulgok, but was headed in a new direction. First of all, Seongho claims that both the Four and Seven are originally manifestations of li and that qi is operated through this actualization of li. In other words, the Four and the Seven are both “li issue/arouse 理發,” not “qi issue/arouse 氣發.” Initially, Toegye tried to articulate the origin and function of li and qi; that is, he argued that, in the case of the Four, qi follows li, and for the Seven, qi arises, and the li rides the qi. Seongho differentiates himself by claiming that “the li issues/arouses and qi follows li 理發氣隨” for both the Four and the Seven. Seongho intended to disprove Yulgok’s theory, which maintained that the Four and the Seven were both ‘qi issue/arouse.’ The problem is that the distinction between the Four and the Seven becomes ambiguous if we follow Seongho’s claim. To solve this problem, Seongho uses a new strategy—distinguishing between the qi of the Four and the qi of the Seven.

Seongho distinguished the Four and Seven concerning the interference of hyeonggi 形氣 or qi of a physical state; physiological energy or power that could negatively influence the psychological state of humans. The Seven contain this extra layer, hyeonggi. From his viewpoint, the Four are nature 性 or li immediately issued/aroused without the mediation of hyeonggi, and the Seven are nature 性 or li issued/aroused through the intermedium of hyeonggi. Thus, while the qi of the Seven has materiality, the qi of the Four does not. In other words, the qi linked to the Four is a psychological or mental energy, and the qi linked to the Seven is a physical one.

It was his disciple Shin Hudam who proposed to distinguish physical qi from cognitive and psychological qi. Shin Hudam argued that the qi in the case of the Four being issued/aroused/is jigakjigi 知覺之氣 or the qi of perception and awareness, and the qi in the case of the Seven being issued/aroused is the qi of the body and its physical operation.15 Seongho actively accepted Shin’s theory as it was close to his and acknowledged Shin’s assertion that the “Jigakjigi does not belong to qi as an individual body and its hyeonggi or physical operation.”16 Furthermore, he newly changed the term and defined jigakjigi 知覺之氣 or the qi of perception and awareness as simgi 心氣 or qi as the heart-mind. In “Jungbal 重跋(The Second Transcript)” of Sachilsinpyeon, Seongho changed ‘simgi 心氣 and hyeonggi 形氣,’ as Shin Hudam mentioned, to jigak 知覺 or awareness/perception and hyeonggi 形氣 or physiological energy.’17

According to Seongho, simgi is the function of the heart-mind when the Four operate, that is, the heart-mind without the intervention of the bodily state or energy, and hyeonggi is when the Seven operates, when there is intervention from the bodily state or energy. In other words, simgi means cognitive operations or mental processes, and hyeonggi refers to the physical energy or power that is distributed throughout the body. Although simgi is also a type of qi originating from the heart (the physical organ), it is a unique state of qi activated only in the mental and cognitive activities of the heart-mind. Again, Seongho calls hyeonggi and simgi daegi 大氣 (comprehensive qi) and sogi 小氣 (particular qi), respectively. According to him, “daegi is the qi that circulates throughout the body and sogi is the qi that is only active in the heart. They are both qi, but there is a difference between big and small.”18 These two have different roles, functions, and places of operation. The distinction between the comprehensive qi and the particular qi is connected to the Four-Seven Debate and other new arguments as it is based on the anatomical structure of the human body, and not merely on functional divisions.19 Interestingly, this anatomical approach was unfamiliar to traditional Confucianism.

Seongho thought that the qi related to the Four and the qi related to the Seven were the same in a fundamental sense, but practically different. Accordingly, he tried to elaborate and build on Toegye’s proposition that the “qi follows” from the passage “the Four is that li issues/arouse and qi follows”, which means that hyeonggi follows li, and that the “qi follows” in the passage “the Seven is that qi arises and li rides qi” means that qi acts as physical energy. If, according to Seongho’s argument, the qi of the Seven refers to the hyeonggi and the qi of the Four refers to simgi, this means that the structure and role of the Four and the Seven can also be clearly distinguished, in accordance with Toegye’s intention. As a result, by dividing qi at a cognitive and physical level, Seongho can classify the Four and the Seven, even while explaining both through Toegye’s frame of “li issues/arouses and qi follows li.” However, his theoretical aims are broader than just giving depth to Toegye’s scholastic tradition or criticizing Yulgok. His distinction between jigak-simgi and hyeonggi cannot be explained by theories of traditional Neo-Confucianism alone. The following section will discuss Seongho’s introduction and use of Western Learning.

4. Matteo Ricci’s Theory of Three Kinds of Soul and Seongho’s Theory of Three Kinds of Heart-Mind

We must first examine Seongho’s theory of three kinds of heart-mind 三心說 to understand the context in which Seongho’s theory goes beyond its traditional Neo-Confucian meaning. The theory of three kinds of heart-mind, a unique theory by Seongho, argues that all things, including humans, have a heart-mind that can be classified into one of three kinds. Seongho elaborates on this idea in his “Simseol 心說” and states that there exists more than one kind of heart-mind in the universe. According to Seongho, there are three kinds of heart-minds: saengjangjisim 生長之心, the mind of being born and growing; jigakjisim 知覺之心, the perceptual/cogitative mind; and uirijisim 義理之心, the rational and moral mind. First, plants have “saengjangjisim.” As with plants, animals also have Saengjangjisim, but unlike plants, animals have a separate jigakjisim. Finally, human beings have uirijisim in addition to saengjangjisim and jigakjisim.

Saengjangjisim in plants denotes the ability or function of being born, growing, and decaying. Jigakjisim refers to a sensory perception that recognizes the cold and feels warmth, or an instinctive ability to like the good and avoid the bad. Finally, uirijisim refers to the ability to reason or make moral judgments. In the case of human beings, Seongho states that jigakjisim can also be classified as insim 人心 (C. renxin), or the human mind, and the uirijisim as dosim 道心 (C. daoxin); the moral mind.

Here, the substantial criteria for classification are the heart as an organ with the ability of perception. Seongho asserts that since xin, or the heart-mind, is a function of the heart, we cannot, strictly speaking, use the expression xin in the context of plants, because they do not have a heart in the sense of the substantive organ. However, unlike inanimate objects such as stone and soil, plants have activity and orientation, so we can use the expression xin for them just as we do for animals and humans who have a physical heart. The ability to perceive is also an important classification criterion. Unlike plants, animals and humans are capable of perceiving external objects, seeking comfort, and avoiding danger, which are all traits of jigakjisim. Seongho admitted that things other than humans can have jigakjisim if they have the ability to perceive the outside world through conscious activities, even at a low level.

Although it was not uncommon in Neo-Confucianism to consider consciousness and moral judgment as traits that distinguish humans from other living things, it was not common to classify all things depending on whether or not it has a heart or the ability to perceive. It was from Xunzi 荀子 that Seongho obtained the idea of this taxonomy, which differs from Neo-Confucianism. According to Xunzi, fire and water have qi, but no life, vegetation has life, but no perception, and birds and beasts have perception, but no morality. However, the human being has qi, life, perception and also morality, so human beings are the worthiest of all.20

Seongho’s idea is very similar to Xunzi. However, Seongho’s new method for taxonomy and the theory of three kinds of heart-mind can hardly be attributed solely to this influence. This is because although Xunzi sought to develop a system of classification for all things, he did not connect this with the concept of xin. A more direct influence can be found in the book of Western Learning that Seongho studied called Tianzhushiyi 天主實義, or The True Meaning of the Lord of Heaven (1603) by Matteo Ricci, who resided in China to spread Christianity in the late 16th century.

One of Matteo Ricci’s essential goals in delivering Christianity to the Chinese was to introduce the theory of soul of Aristotle and Thomas Aquinas. To this end, he devised a new term, linghun 靈魂, or the rational soul, by combining the Chinese terms ling 靈, or intelligence, and hun 魂, or soul.

In this world, there are three kinds of soul. The lowest is called the life principle—the vegetative soul. This kind of soul supports vegetation in its growth, and the soul is also destroyed when it withers. The second class of soul is called the sentient soul. Birds and beasts possess this soul. It allows the birds and beats to be born, develop, grow up, etc. The most superior of the souls is called the intellectual soul. This is the human being’s soul, which includes (the powers of) the vegetative and sentient souls. It enables people to grow to maturity; it causes people to be aware of things outside themselves, and it allows people to infer the nature of things and distinguish between one principle and another.

(Ricci 1985, pp. 144–45)

In Scholasticism, souls are the principle and cause of life and are classified into three categories according to their levels. First, shenghun 生魂, or the vegetative soul, is that with the ability to take in nutrition and grow; juehun 覺魂, or the sensitive soul, possesses sense awareness and athletic ability; and finally, linghun 靈魂, or the rational soul, possesses cognitive faculties such as thought, perception, and feeling. The ability of nutrition and generation belongs to plants, and all animals have the perceptive ability and the ability of nutrition and generation, but only humans have the rational ability in addition to these. Seongho also categorizes plants, animals, and human beings in a similar way.

Among researchers, there were varying opinions on whether the new classification system was derived from Xunzi’s system or whether Western Learning influenced it. This is because Seongho does not explicitly mention Western Learning in “Simseol”. However, in order to confirm the influence of Western Learning on Seongho’s theory of the three kinds of heart-minds, the problem must be approached from within a broader context. First, traditional Neo-Confucian scholars rarely incorporated Xunzi’s theory of the heart-mind into their thoughts. Therefore, the use of Xunzi’s ideas is, by itself, a conscious new approach by Seongho.

There is concrete, documented evidence of the theoretical inspiration that Western Learning gave to Seongho in Seonghosaseolyuseon 星湖僿說類選, or The Selected Essays from Seonghosaseol, an abridged version of Seonghosaseol by Ahn Jeongbok 安鼎福 (pen name Sunam 順庵; 1712–1791), one of Seongho’s disciples and a core member of the Seongho school. Seonghosaseolyuseon contains the deleted contents of Seonghosaseol, introduces Xunzi’s theory, and mentions a Jesuit Francesco Sambiasi (畢方濟, 1582–1649), the author of Lingyanlishao 靈言蠡勺, or Humble Attempt at Discussing Matters on the Soul (1624).21 It is very likely that Sunam erased the problematic parts of his master’s text. This is particularly credible because Ahn edited Seongho’s works after the national oppression against Western Learning and Catholicism began.22

In conclusion, it can be inferred that Seongho read Western Learning books such as TianzhuShiyi and Lingyanlishao on the topic of the theory of soul, and then connected these ideas to similar theories of Xunzi, thereby transforming the theory of three types of soul into the theory of three types of heart-mind. The reason why Seongho adopted the theory of three types of soul was to explain the mechanism of human morality. For Seongho, Dosim stemming from Uirijisim serves as a distinctive feature that differentiates humans from other beings. He asserts that humans are the only beings in the universe who can truly perceive and understand.

However, the most interesting part of the theory of the three types of heart-mind lies in the concept of jigak 知覺 (C. zhijue), or “the cognitive function of mind”, which Seongho advocates using as a standard for differentiating plants, animals, and human beings. Seongho says, “xin is jigak,”23 which means xin refers to the ability to perceive. To Seongho, xin means conscious activity, including sensory perception. From this standpoint, Seongho regards jigak as the ability to perceive and uses it as the point of differentiation of all things, thus combining animals and human beings, who have the ability to perceive and perform conscious activity into one category, and Heaven, Earth, stone, and vegetation, which have no perception, into another.

This is different from Zhuxi’s position, who uses the expression tiandizhixin 天地之心, or the heart-mind of Heaven and Earth, and claims that the universe has the qualities that constitute a personality. Whether or not Heaven and Earth have heart-minds was one of the biggest debates among Zhuxi and his disciples. Zhuxi argues that Heaven and Earth do not have heart-minds to act, and therefore do not consciously think and act, but they have a kind of “heart-mind” in terms of delivering moral value by endlessly creating all things.24 A more controversial issue is the meaning of jigak.

In the context of Neo-Confucianism, jigak is used in a multi-layered sense. First, jigak can be used to mean sensory perception depending on the situation. Neo-Confucians used the term jigak to express both a superficial dimension of sensory perception and also an in-depth dimension of metaphysical awareness. They used jigak to mean not only perception, but also the principle or the ability to perceive.25 Even if the meanings of jigak/zhijue are multi-layered, ultimately, Zhuxi and his successors focused on the meaning of metaphysical awareness or the principle that enables perception at the fundamental level. However, Seongho differentiates himself by viewing sensory perception and the spontaneous activity of pursing life and avoiding death, as jigak. In this context, jigak is a kind of perception and consciousness. In Seongho’s framework, the concept of jigak leaves its network of traditional Neo-Confucian meaning.

The theory of three types of heart-mind worked as a theoretical device to systematically explain the characteristics and structure of human consciousness. However, it is possible to use the expression xin to describe the heart-mind of unconscious objects such as plants and Heaven and Earth, including instinctive reactions and desires responding to the external stimulus of living things. However, in Seongho’s theory, the more precise meaning of xin is related to human morality. The original goal of Neo-Confucianism was to explain human morality, but the innovative aspect of Seongho’s theory of three kinds of heart-mind lies in the fact that it connects the foundation of moral ability with jigak as the perception of the external world.

What is more interesting is that Seongho attempts to explain consciousness through the physical evidence of the organ and its structure. There are two human organs that Seongho regards as the physical foundation of jigak: the heart and the brain. Seongho distinguishes ji 知, or knowing/reasoning, and gak 覺, or perception, from jigak, and defines each of their roles as follows.

Because human beings have a brain, they immediately flinch before thinking and judging when an external thing stimulates it. It is the brain’s work to respond to stimuli, and it is the heart-mind’s work to think, know and judge when stimulated by things. If so, the unconditionally responsive awareness gak 覺 is in the brain, and the knowing or reasoning ji 知, which is the ability to think and judge, is in the heart.

(“Seogugui”)

This explanation was unfamiliar to Confucian scholars because the foundation of human mental activity was considered to be xin. The medical textbooks that originated from the Daoist tradition considered the brain an essential organ for life but did not link the brain to the conscious activity of a human being. Thus, Seongho’s stance on the Four-Seven Debate deviates from the traditional Neo-Confucian theories. If the simgi 心氣, which stems from the Four, refers to jigakjigi 知覺之氣 or qi of awareness and perception, then it differs from traditional Neo-Confucianism in that it involves a cognitive process that responds to sensory stimuli in the brain as a physical organ.

How did Seongho introduce the concept of the “brain,” which is unfamiliar to the Neo-Confucianism tradition, as the subject of perception? The answer is in the book called Zhuzhiqunzheng. The next chapter will take a closer look at the brain, perception, and the heart-mind.

5. Understanding and Using Brain Theory through Zhuzhiqunzheng

Even though Seongho had believed, in accordance with traditional Confucianism, that it is the heart-mind that supervises thought and judgment, he came to believe that it is the brain that controls the reaction to external stimuli and activity. Seongho tried to distinguish jigak 知覺 from the physical mechanism by assigning ji 知and gak 覺 to the heart and brain, respectively.

It is Zhuzhiqunzheng that provided the intellectual stimulation for Seongho to understand jigak as a dualistic structure—the brain, which accommodates and processes sensory perception, and the heart-mind, which governs final judgment and execution. Zhuzhiqunzheng is not a general book on theology, but a book to prove the providence of God through natural phenomena and natural science. The text itself is Johann Adam Schall von Bell’s (湯若望, 1592–1666 hereafter Adam Schall) translation of De providential numinis et animi immortalitatelibri duo adversusatheos et politicos (Aantwerp: Plantin, 1613, hereafter De providential numinis) written in 1613 by a Belgian Jesuit, Leonardus Lessius (1554–1623).

Furthermore, it is significant that Zhuzhiqunzheng is not a faithful translation of De providential numinis, but a new book edited and rewritten by Adam Schall for the purpose of the Chinese mission in the 17th century. Adam Schall’s intention behind the translation was to prove that all of God’s creatures have both providential and teleological purposes for God. Therefore, to show divine providence, this book explains anatomical principles and physiological knowledge of the human body as additional evidence of natural theories from fields such as meteorology and astronomy.26 Among these, Seongho’s interest was stimulated by Section 5, which introduces the physiological–medical knowledge of the human body from the perspective of Galen, an ancient Greek physician, surgeon, and philosopher.

Galen was known as the scholar who developed Greek medicine by combining the humoral theory of Hippocrates, and the teleology of Aristotle.27 Galen’s methodology, which teleologically recognizes every part and function of the human body, was a fitting way to explain the creation of human beings by God to the Jesuits. Section 5, in this context, deals with “an explanation of human anatomy and physiology, especially the intricate network of bones, veins, arteries, and nerves, to show that a divine being must have created this.” (N. Standaert 2001, p. 790). It contains detailed physiological explanations about the functions and roles of each part of the human body, concentrating on the heart, brain, and liver. It also introduces anatomical knowledge about bones and muscles, the principle and role of blood production, and the structure and activity of the nervous system.

Physiology and medical knowledge about the human body was hardly the primary topic of inquiry for scholars of Neo-Confucianism. Therefore, the attention Seongho gave to Zhuzhiqunzheng was intentional and selective. He studied unfamiliar Western medicine and physiology to renew his theory. At this point, there is something to be careful about of when analyzing Seongho’s use of the Zhuzhiqunzheng, and that is viewing Seongho’s study of the Zhuzhiqunzheng as acceptance of modern Western medicine by pre-modern East Asia. However, the physiology and medical information in Zhuzhiqunzheng was far from the latest theory in Europe at that time.28

The Jesuit Leonardus Lessius was not interested in introducing the latest theories of medicine but in commenting on natural phenomena as evidence of an Aristotelian teleological view of the world, and this is the same reason why Adam Schall translated this book. Their goals and methods do not go beyond the medieval worldview. In this context, it is not significant how much more “advanced” information from the West is contained in this book compared to East Asian traditional knowledge. We need to examine the question: “Which parts of this book, resonated with the intellectuals of China and Joseon and why?” Seongho’s understanding and utilization of Zhuzhiqunzheng may be a suitable answer to this question.

There is a problem to be examined more carefully. Seongho’s introduction of Zhuzhiqunzheng should not be understood as a unilateral acceptance of Western Learning. When Adam Schall translated European naturalistic and physiological concepts into Chinese, he decided to borrow traditional Chinese vocabulary and concepts to make it easier for Chinese intellectuals to understand. A typical example is qi. Adam Schall uses qi as a translation of the Greek concept pneuma. According to this translation method, European knowledge was mixed with Chinese knowledge. The initiative to understand and utilize these terms or theories did not come from the translators but from the intellectuals of East Asia, including Seongho.

There is also something that needs to be noted about the motive, purpose, and utilization of the book. Seongho’s research of the Zhuzhiqunzheng’s theory is often evaluated in terms of whether or not he had accepted Western medicine or how much he understood this foreign resource. However, Seongho did not accept information from Zhuzhiqunzheng as medicine or physiology as such. Seongho had no interest in physiology or medicine itself.29 Rather, he utilized brain theory based on the traditional viewpoint of the theory of heart-mind. In Joseon, not only Seongho but later scholars such as Dasan and Yi Gyu-kyung (李圭景, 1788–1860) also showed interest in Section 5 of the book. Yet, the two scholars are distinguished from Seongho’s approach in that they studied this chapter in the context of medicine, and not in terms of the theory of heart-mind.30

Then, our question should be: What intellectual stimulation did Zhuzhiqunzheng provide Seongho? Through this intellectual stimulation, what did Seongho transform about the Neo-Confucianism theories that he inherited, and how? There are two points to be noted about Seongho regarding the physiology–medical theory introduced in Zhuzhiqunzheng. One is that Galen sought to construct a theory that criticized the cardio-centric view of the heart from ancient Western medicine and established the brain as the regent (hegemonikon) of the body.31 The other is that a complex element called pneuma plays an essential role in the operation of the human body, especially in the brain.

Since Aristotle described pneuma as a critical element of the body and the sanguineous system, pneuma has been regarded as one of the core concepts of ancient medical theory. In ancient Greece, pneuma meant “breath” or “vital spirits”, and also the active, generative principle that organizes everything in the universe. Interestingly, pneuma has divine properties compared to the other four elements.32 Galen also introduced pneuma into his physiological and pathological formulations,33 specifically explaining the role of pneuma in connection with brain activity. At this point, Galen’s study of the brain differs from our modern understanding of it. (Johnstone 2006, p. 19)

What is interesting about Zhuzhiqunzheng is that he translated pneuma, a key term that explains the structure of the natural world, the human body, and, furthermore, mental activity, using the Chinese concept of qi. The qi, a traditional concept handed down from ancient China, is also a complex concept used to express life force or human emotion that is a component of matter yet simultaneously cannot be reduced to it. This is the same with the concept of pneuma, which was also used to explain the brain and psychological activities. (van der Eijk 2005, p. 132) Adam Schall used the term qi as a phenomenon related to the air, such as rain, snow, wind, and frost, but acknowledged some of the traditional meanings of the term by using it as a translation of Galen’s pneuma, which includes both attributes of mind and matter. This eclectic translation would have played a role in reducing the rejection of Zhuzhiqunzheng by East Asian intellectuals.34

Adam Schall’s attempt exemplifies an important feature of medieval scholarship, which is that the fields of philosophical psychology and physiology–medicine that are separated from the modern point of view are integrated in the medieval context. This feature is more apparent when compared with another book of Western Learning, Xingxuecushu 性學觕述, or Cursory Discussion on Human Nature (1624)35, which also deals with the theory of soul. Xingxuecushu, written by the Italian Jesuit Giulio Aleni (艾儒略, 1582–1649), begins with an introduction to the soul, but later deals with the medical and physiological contexts of Aristotle and Galen’s theories. This book synthesizes Aristotle’s two books: the first half is an excerpt and translation of De anima, and the second is an excerpt and translation of Parva naturalia. (Giulio Aleni 2020, p. ix) Of these two, Parva naturalia is similar to Zhuzhiqunzheng’s Section 5 in that it deals with natural phenomena common to body and soul such as senses, memory, sleep and dream, and life and death in a physiological context.

Lingyanlishao 靈言蠡勺 (1624), where Seongho was introduced to the idea of brain theory, has a similar context. Based on Aristotle’s De anima, Lingyanlishao follows traditional Scholasticism and explains human mental activity by dual compartmentalization where the brain is responsible for perception and memory, and the soul is responsible for rational judgment. In particular, this book introduces memory as one of three functions of the soul, along with reason and desire. Memory is again divided into two: rational memories that record the types of things are stored in the soul, while emotional memories are stored in the brain. According to these explanations, the brain is in control of a part of the mental activity of human beings.

Interestingly, De anima, which inspired Lingyanlishao, does not provide physiological information about memory. Lingyanlishao is based on Aristotle’s theory of the soul, but the content of memory and reminiscence is from the physiological parts of Parva naturalia, not De Anima. In order to introduce the theory of soul to Chinese intellectuals, Sambiasi, who translated this book, also combines philosophical psychology and physiology. For medieval scholars, physiology and medicine were ultimately part of theology. In this way, Xingxuecushu and Lingyanlishao can be regarded as providing comprehensive theories on human beings, encompassing theories on both human rationality and physiology. Zhuzhiqunzheng’s explanations of the human body are not limited to medical theory as it is based on the structure and activity of the soul. The human being at that time was viewed primarily of rationality, but was considered to be a more multi-layered, complex being that included physiological traits.

As a result, in the Western Learning books that Seongho read, subjects such as the theory of the soul from Aristotle and Thomas Aquinas, and physiology and medicine from Aristotle and Galen, coexist. This is probably what caught Seongho’s interest. One of the theoretical goals of Neo-Confucianism was to integrate the natural world of qi with the ideological realm of li, and their interpretation of the human being was a result of it. However, most Neo-Confucian scholars have long undervalued biological and physiological theories, focusing on improving moral practice through pure principles without materiality.

Seongho, however, showed great interest in the body’s physiological structure and the energy that manages the body. After studying Zhuzhiqunzheng, Seongho used physiology and anatomical knowledge to explain the integration of these two subjects on a practical level. Zhuzhiqunzheng lists the anatomical knowledge of the human body and then summarizes the physiological information about the body’s operation as follows.

The form of the body exists because there are bones and flesh. However, innate heat is essential for generation, blood for nutrition and growth, and qi for motion and sense. For this reason, when the Lord of Heaven created human beings, he first created three organs to rule within the body: the heart, liver, and brain. All the other organs move according to their command.

(“Yirenshenxiangzhi”)

The key here is heat, blood, and qi. Heat is the source of life, and blood is needed for the circulation of nutrition. The phrase qi in this excerpt refers to pneuma, one of the core concepts of ancient Greek medicine. Zhuzhiqunzheng explains the operating principle of the human body, connecting the liver, heart, and brain, and regards the brain as the nerve center, based on Galen’s theory that criticizes Aristotle’s cardiac centrism. First, the liver produces tixingzhiqi 體性之氣 (pneuma physicon), or the natural spirit; the heart produces inner heat and shengyangzhiqi 生養之氣 (pneuma zoticon), or the vital spirit, and the brain produces microscopic dongjuezhiqi 動覺之氣 (pneuma psychicon), or the animal spirit. Some parts of the vital spirit made in the heart enter the brain along the aorta, becoming the more refined animal spirit. This animal spirit commands all sensory organs to perform all the exercises and tasks of the senses.

Here, Seongho is particularly interested in dongjuezhiqi 動覺之氣 (K. donggakjigi), which is responsible for the brain’s sensation and reaction to outside stimuli. He acknowledges that the brain is the master of the whole body because it is the brain that reacts when the flesh touches external objects. In particular, Seongho admits the difference between Western theory and Confucianism, observing that the Western theory uses the concept of gak/jue 覺 originating from the brain. Consequently, Seongho understood the brain’s physical mechanism of receiving and responding to stimulation as the core of human conscious activity. However, Seongho’s introduction of brain theory was not meant to replace the function of xin in Neo-Confucianism. Seongho acknowledged the theory that the brain was the center of stimulation, reaction, and movement to explain the function of xin in a practical way. The conclusion of “Seogugui”, that “sensation is the function of the brain and knowing the sensation is the function of xin”, illustrates this point.36

At this point, the role of the brain was gak 覺(perception) of external stimuli, while the traditional heart-mind was considered the subject that makes the ultimate judgment and decision. Seongho inserts the brain into the operating mechanism of the heart-mind as the subject of perception/awareness. In conclusion, Seongho hypothesized that the brain as another physical component that accompanies xin in the process of describing human consciousness. Thus, if the brain controls perception, it differs from the general principles of Neo-Confucianism, which views the psychological state of human beings as a manifestation of li.37

A careful approach is required at this point. The existing research propounds that Seongho reflects modern development by recognizing the brain as the main organ of human action and reason.38 However, Seongho only uses the brain theory partly, and basically does not change the status of the brain and heart-mind. More importantly, the role of the brain was limited even in the book of Western Learning that Seongho referred to. Adam Schall, as well as any European people of his time, did not regard the brain as the subject of human mental activity. Even in Thomism, the brain is responsible only for accepting external stimuli or storing memories obtained through sensory organs, while human mental activity and thought are considered to be the responsibility of the rational soul. Just as the rational soul dominates human mental activity in Thomism, the heart-mind plays the same role in Seongho’s thought. Therefore, it is necessary to be wary of overstating the significance of his understanding of brain theory or regarding it as a sign of modernization.

Both Seongho and the Jesuits did not separate the human body structure and theory from each other, and did not completely separate physiology and soul theory. In such a context, there is no reason for Seongho, who came from a tradition that has never treated physiology–medicine as a legitimate or even a subordinate theory of heart-mind, to place the brain over the heart-mind, since it lies subordinate to the soul in the materials he referenced.

6. Reinterpretation of Zhijue 知覺 and Change in the Meaning of Weifa 未發

The radical changes caused by Seongho’s new interpretation of jigak—as a state of daily consciousness according to the stimuli and reactions of the brain—are seen in the theory of weifa-yifa 未發已發論. Originally found in Zhongyong, weifa 未發(K. mibal) refers to the state in which the Seven have not yet been aroused, and yifa 已發 (K. ibal) refers to the state in which emotions have been aroused after one’s contact with the outside world. In the state of weifa, maintaining equilibrium 中 without being partial is considered the ideal state, whereas in yifa, displaying emotions properly to achieve harmony 和 is considered the ideal state.

In Neo Confucianism, weifa is not merely a state of unconsciousness or pre-consciousness, but a state of metaphysical stability or equilibrium. Meanwhile, yifa is a state of balance, or harmony, and expresses emotions in response to external stimuli. Weifa is regarded as an entirely moral state in itself because its metaphysical value is unimpaired. By comparison, yifa could be morally good or bad since emotions have already been expressed outward following contact with the outside world. What was problematic for Neo Confucian scholars was “could it be moral even after emotions are aroused?”

Interestingly, in Simgyeongjilseo, Seongho redefines weifa through the context of jigak/zhijue. He insisted that the operation of consciousness itself cannot be immediately regarded as the yifa state, because the operation of consciousness is not yifa unless it is a concrete calculation or judgment in a strong sense. In Seongho’s context, jigak means sensory perception, not the principle or ability of perception, unlike the Neo-Confucian theory of weifa and yifa. In “Jigak 知覺” of Seonghosaseol, Seongho argues that even when the senses generate perceptions that result in cognitive function, the weifa state occurs only when active thoughts or intentional judgments begin.

The heart-mind is inherently intelligent. When there is something in front of us, we cannot help but see that it is white or black, round or square, as if things are reflected in a mirror. Even though we know something is black or white, round or square, if we do not feel emotions such as love or hate towards the object, it is considered ibal. If we are in the state of yifa everytime we encounter things, there would be no case where the heart-mind is in the state of weifa.

(“Jigak 知覺”)

Seongho does not imbue jigak/zhijue itself with moral meaning. He considers the whole process of perception–recognition–judgment as weifa. At this point, yifa is determined not by whether perception, recognition, or thoughts exist, but by whether moral judgments are made. In other words, the moment when moral judgments and decisions are made is yifa in its true sense.

If we acknowledge, as Seongho did, that yifa does not refer to conscious perceptual activities but to the moment of moral judgment and conscious intervention, the relationship between weifa and yifa must be regarded as the relationship between the operation of physical perception or cognition and rational judgment or moral practice. In this theoretical framework, what is critical is the rational judgment and moral decision-making in the state of yifa, not the “preservative nurturance” in the state of weifa.

Seongho wanted to regard human moral practice as sequential steps that lead to perception–recognition–decision–practice, rather than as a tranquil and convergent effort to preserve the metaphysical realm. In Seongho’s perspective, moral practice is not the process of static cultivation that maintains an introverted and convergent attitude, but the result of the concrete and active moral determination that requires moral judgment and decision-making at every moment of everyday life. As a result, Seongho’s reinterpretation of the concept of yifa weakened the metaphysical character of the theory of weifa and yifa and moved the focus to the human mind’s perception, judgment, and practice.

7. Conclusions

By adopting the Western theory that the brain is the foundation of cognitive function, Seongho went beyond the Neo-Confucian way of explaining the mind based on a transcendental dimension, and he attempted to integrate body, perception, reason, and moral judgment by connecting the characteristics and abilities of the heart-mind with the organs of the human body. He could go beyond the theoretical limitations of Neo-Confucianism, which explains the relationship between human mental activity and the body speculatively or figuratively. He intended to provide a basis for explaining the morality inherent in human beings while understanding the concrete physical basis of human mental activity. In conclusion, his interpretation of jigak/zhijue can be regarded as a selective and consecutive process that leads the mechanism of moral awareness and practice to perception–cognition–judgment–decision–practice.

Unlike other Neo-Confucian scholars of Joseon, Seongho paid due attention to the biological and physiological foundations of xin 心, or the heart-mind. This theoretical transformation was mediated by Western Learning. It does not mean that Seongho’s philosophical acceptance of Western Learning has crossed the boundary of Confucianism or Neo-Confucianism. Seongho did not just accept or follow the theory he inherited from Toegye, but widened the boundaries of Confucianism by actively utilizing the ideological resources available to him at the time through Western Learning. Seongho developed his theory by the selective introduction of some Western Learning content that stimulated his philosophical thoughts.