The study of Yi contains the I Ching itself and all the results of human research on the I Ching.

From the Han Dynasty onwards, a group of scribes who specialized in the study of the Book of Changes appeared. They either made annotations, or expounded righteousness, or excavated elephants, and gradually formed "easy learning".

The profound connotation of "righteousness" and "number of images" unique to the Book of Changes, the scholars of Yi have different opinions in the past dynasties, forming various views and schools, and the most influential ones are mainly divided into two camps: the number of images and the school of righteousness.

The Yili School of Yi Xuexue is to further elaborate and apply the "Book of Changes" and "Book of Changes", and use them to explain the changes in personnel and heaven, as well as use the "Classics" and "Biography" to explain the principles of self-cultivation and governing the country and leveling the world.

The Xiangshu School generally refers to those masters who can pinch and calculate in Chinese history, such as Jiang Ziya, Fan Li, Wen Chong, Zhang Liang, Zhuge Liang, Seng Yixing, Liu Bowen and so on.

From the "Book of Changes" like mathematics developed a school is also called "mathematics", the number is also a politician, military strategist, strategist, thinker compulsory course, simply summarized there are physiognomy, feng shui, stargazing, eight characters, dreams, six yao, occupancy, word measurement, six ren, qi men and other subjects, in addition to traditional Chinese medicine, health and other disciplines, it can be seen that the so-called "elephant number school", most of them are some doers.

The sum of the two schools of elephant number and righteousness is "easy to learn", and the image, number, reason, and occupation in "easy to learn" are a whole, if you can only speak the Tao and only understand one or two of them, you cannot be called proficient in "easy learning".

Metaphysics was the main philosophical trend developed in the Wei and Jin dynasties with the Lao Zhuang doctrine as the core. Metaphysics, that is, the study of Xuanyuan, refers to the two aspects of words and deeds, and most of them are subtle in their words, and their actions are far-reaching and far-reaching.

This school calls "Zhou Yi", "Laozi", and "Zhuangzi" the "Three Xuan". Metaphysicians used their reformed Lao Zhuang Thought to annotate Confucian works such as "Analects" and "Zhou Yi", which reformed the cumbersome scriptures of the Han Dynasty, which was an important school in the history of Yi Studies.

The founder of the metaphysical school of Yixue was Wang Bi, who annotated the "Zhou Yi" from a metaphysical point of view; Wang Bi's "complacent" style of interpreting Yi opened a precedent for later generations to interpret "Zhou Yi". At that time, there were also He Yan, Ji Kang, Ruan Ji and others.

The emergence of Wei and Jin metaphysics was based on the decline of Confucianism in the Han Dynasty and made up for the shortcomings of Confucianism; It is evolved and developed from the Taoist thought of the Han Dynasty and the study of Huang Lao.

Later, the connotation of metaphysics was continuously expanded, and five systems including mountain, medicine, life, divination, and physiognomy were produced.

Mountain, the content of which refers to self-cultivation, meditation and internal refining, etc., mainly includes: guidance, inner Danshu, outer Danshu, martial arts, etc.

Medicine is the ancient Chinese medicine system, and the treatment methods are divided into: acupuncture, decoction, massage, blessing, prescription treatment, etc.

Life, that is, numerology, is the knowledge of calculating the fate of life, including eight characters, Ziwei, star destiny, etc.

Bu, that is, divination, mainly includes: Taiyi, Liuren, Qimen, Liuyao, plum blossoms, etc.

Phase, for physiognomy, there are phase earth (feng shui), physiognomy (face reading, palmistry, bone physiognomy) and so on.

From the introduction of Yixue and metaphysics, it can be seen that Yixue contains a wider range of academic content, and metaphysics is a philosophical school of Yixue, so the two are both related and different.

It can be said that "easy learning" refers to all the knowledge and learning about "easy", and "metaphysics" refers to a school of technology in "easy learning", which is good at "art" and relatively narrow in scope.