Zhu Xi or Chu Hsi (born October 18, 1130, Yuxi, Fujian province, China – died April 23, 1200, China) was a Song Dynasty (960-1279) Confucian scholar who became the leading figure of the School of Principle and the most influential rationalist Neo-Confucian in China. His contribution to Chinese philosophy included his grouping of the Four Books, his emphasis on the investigation of things (gewu), and the synthesis of all fundamental Confucian concepts.

Life

Teachings
During the Song Dynasty, Zhu Xi's teachings were considered to be unorthodox. Rather than focusing on the Book of Changes like other Neo-Confucians, he chose to emphasize the Four Books: the Great Learning, the Doctrine of the Mean, the Analects of Confucius, and the Mencius as the basis for his philosophy. For all these classics he wrote extensive commentaries that were not widely recognized in his time; however, they later became accepted as standard commentaries. The Four Books served as the basis of civil service examinations through to 1905.

The Four Books
He argued that all things are brought into being by two universal elements: qi, translated as vital (or physical, material) force; and li, translated as rational principle (or law). The source and sum of li is the Taiji (Wade-Giles: Tai Chi), meaning the Great Ultimate.
According to Zhu Xi's theory, every physical object and every person contains li and therefore has contact with the Taiji. What is referred to as the human soul, mind, or spirit is defined as the Taiji, or the supreme regulative principle at work in a person.
Qi and li operate together in mutual dependence. These are not entirely non-physical forces; one result of their interaction is the creation of matter. When their activity is rapid the yang energy mode is generated, and when their activity is slow, the yin energy mode is generated. The yang and yin constantly interact, gaining and losing dominance over the other. This results in the structures of nature known as the five elements (fire, water, wood, metal, and earth).
In terms of li and qi, Zhu Xi's system strongly resembles Buddhist ideas of li (again, principle) and shi (affairs, matters), though Zhu Xi and his followers strongly argued that they were not copying Buddhist ideas. Instead, they held, they were using concepts present in the Book of Changes.
Zhu Xi discussed how he saw the Great Ultimate concept to be compatible with principle of Taoism, but his concept of Taiji was different from the understanding of Tao in Daoism. Where Taiji is a differentiating principle that results in the emergence of something new, Dao is still and silent, operating to reduce all things to equality and indistinguishability. He argued that there is a central harmony that is not static, empty but dynamic, and that the Great Ultimate is in constant movement.

Vital force (qi), principle (li), and the Great Ultimate (taiji)
Zhu Xi considered the earlier Confucian Xun Zi to be a heretic for departing from Mencius' idea of innate human goodness. Even if people displayed immoral behaviour, the supreme regulative principle was good. It is unclear whence exactly immorality arises; Zhu Xi argued that it comes about through the muddying effect of li being shrouded in qi, but this does not fully answer the question, as qi itself shares part of the Taiji.

Human nature
According to Zhu Xi, knowledge comes first, but action is more important. This is in contrast to Wang Yangming's doctrine of the unity of knowledge and action.

The investigation of things and the extension of knowledge
Zhu Xi did not hold to traditional ideas of God or Heaven (Tian), though he discussed how his own ideas mirrored the traditional concepts. He encouraged an agnostic tendency within Confucianism, because he believed that the Great Ultimate was a rational principle, and he discussed it as an intelligent and ordering will behind the universe. He did not promote the worship of spirits and offerings to images. Although he practiced some forms of ancestor worship, he disagreed that the souls of ancestors existed, believing instead that ancestor worship is a form of remembrance and gratitude.

Religion
Zhu Xi practiced a form of daily meditation similar to, but not the same as, Buddhist dhyana or chan ding (Wade-Giles: ch'an-ting). His meditation did not require the cessation of all thinking as in Buddhism; rather, it was characterised by quiet introspection that helped to balance various aspects of one's personality and allowed for focused thought and concentration.
His form of meditation was by nature Confucian in the sense that it was concerned with morality. His meditation attempted to reason and feel in harmony with the universe. He believed that this type of meditation brought humanity closer together and more into harmony.

Meditation
Zhu Xi heavily focused his energy on teaching, claiming that learning is the only way to sagehood. He wished to make the pursuit of sagehood attainable to all men.
He lamented more modern printing techniques and the proliferation of books that ensued. This, he believed, made students less appreciative and focused on books, simply because there were more books to read than before. Therefore, he attempted to redefine how students should learn and read. In fact, disappointed by local schools in China, he established his own academy, White Deer Hollow Academy, to instruct students properly and in the proper fashion.

On teaching, learning, and the creation of an academy
Zhu Xi wrote what was to became the orthodox Confucian interpretation of a number of concepts in Taoism and Buddhism. While he appeared to have adopted some ideas from these competing systems of thought, unlike previous Neo-Confucians he strictly abided by the Confucian doctrine of active moral cultivation. He found Buddhist principles to be darkening and deluding the original mind

Taoist and Buddhist influence on Zhu Xi
From 1313 to 1905, Zhu Xi's commentaries on the Four Books formed the basis of civil service examinations in China. His teachings were to dominate Neo-Confucians such as Wang Fuzhi, though dissenters would later emerge such as Wang Yangming and the School of Mind two and a half centuries later.
His philosophy survived the Intellectual Revolution of 1917, and later Feng Youlan would interpret his conception of li, qi, and taiji into a new metaphysical theory.
He was also influential in Japan known as Shushigaku (朱子学, School of Zhu Xi), and in Korea known as Jujahak (주자학), where it became an orthodoxy.

Zhu Xi's influence

Life magazine ranked Zhu Xi as the forty-fifth most important person in the last millennium. Trivia

Confucianism
Neo-Confucianism
Wang Yangming
Wang Fuzhi
Feng Youlan
Yuelu Academy
White Deer Grotto Academy
Classical chinese writers
Fujiwara Seika -- Japanese disciple of Zhu Xi
Hayashi Razan -- Seika's student & Tokogawa political theorist
Hayashi Gahō -- Tokugawa academician/scholar/bureaucrat Further reading

Chan, Wing-tsit. Reflections On Things at Hand, New York, 1967.