Two antagonistic currents of thought manifested themselves at an early date in the history of Chinese philosophy and run throughout its entire course. One is represented by the Yijing and Confucius (551–479 B.C.),  the other by Laozi .  The former advocated a dualism and showed agnostic, positivistic, and practical tendencies, while the latter was monistic, mystical, and transcendental.
Dualism was the first speculative philosophy ever constructed by Chinese thinkers. It is set forth in one of the oldest writings, called Yijing, “Book of Changes .” The book is, however, the most unintelligible, most enigmatical document ever found in Chinese literature. Many conflicting theories have been advanced as to its real value and meaning, and we have not yet come to any definite settlement. As far as I can judge, its true significance had been entirely lost even as early as the beginning of the Zhou dynasty. Not being able to determine its exact nature, King Wen (1231–1135 B.C.) and Lord Zhou (who died 1105 B.C.) took it for a sort of general treatise on natural phenomena and human affairs, and upon this surmise they wrote some commentary notes which imply suggestions of practical wisdom and moral instructions. Some four hundred years later, Confucius again struggled hard to arrive at a definite and true estimate of the book. He seems to have been not wholly satisfied with the practical interpretation of it by Wen and Zhou. He wished to find a speculative philosophical foundation in the apparently confusing and enigmatic passages of the Yijing. He is said to have expressed his earnest desire to have his life prolonged several years, so that he could devote them exclusively to the study of this mysterious literature. The “Appendices”  popularly ascribed to Confucius contain some philosophical reflections, and on that account some later exegetists declare that the Yijing was primarily a philosophical treatise and later transformed into a book of divination. Whatever the true nature of the book, it is from this that early Chinese thinkers derived their dualistic conception of the world.
Some lexicographers think that the character yi is made of “sun” and “moon .” Whether this be the real origin of the character or not, the interpretation is very ingenious, for yi means change in any form—the change from daylight to moonlight night, the change from blooming springtime to harvesting autumn, or the change from fortune to ill luck and vice versa. Change is a predominant characteristic of all existence; and this is caused by the interplay of the male (yang ) and the female (yin) principles in the universe. According to the interaction of these opposite forces, which in the Yijing proper are called Qian and Kun and represented respectively by a whole line and a divided line, beings now come into existence and now go out of it, and a constant transformation in the universe takes place.
So it is said in Appendix III (see Legge , p. 348 et seq.):
Heaven is high, earth is low; and [the relation between] ] the strong (qian) and the weak (kun) is determined. The low and the high are arranged in order, and [the relation between] the noble and the lowly is settled. Movement and rest follow their regular course, and [the relation between] the rigid and the tender is defined.
Things are set together according to their classes; beings are divided according to their groups; and there appear good and evil. In the heavens there are (different) bodies formed; and there take place changes and transformations.
Therefore, the rigid and the tender come in contact; the eight symbols interact. ] To stimulate we have thunder and lightning. To moisten we have wind and rain. The sun and moon revolve and travel, which give rise to cold and warmth.
The strong principle makes the male, and the weak principle makes the female. By the strong the great beginning is known, and weak brings beings into completion. The strong principle becomes intelligible through changes; the weak principle becomes efficient through selection. The changing is easy to understand. Selection is easy to follow. As it is easy to understand, there grows familiarity: as it is easy to follow, efficiency is gained. That which is familiar will last: that which is efficient will be great. Lasting is the virtue of a wise man; great is the accomplishment of a wise man. Through change and selection is obtained the reason of the universe. When the reason of the universe is obtained, the perfect abides in its midst.
Again, Confucius says in Appendix IV (see Legge, p. 395): “The strong and the weak are the gates of change. The strong is the male gender, and the weak is the female gender. When the male and the female are united in their virtues, the rigid and the tender are formulated, in which are embodied all the phenomena of heaven and earth, and through which are circulated the powers of the spirits bright.”
To make another quotation, in which the gist of the dualistic conception of the Yijing is more concisely stated (Appendix VI; see Legge, p. 423): “In olden times when the wise men made the Yi, they wanted it to be in accord with the nature and destiny of things, which is reason. Therefore, they established the heavenly way in Yin and Yang; they established the earthly way in tenderness and rigidness; they established the human way in humaneness and righteousness. Thus, each of the three powers of nature was made to be controlled by a set of two principles.”
Whatever we may call them, the strong and the weak, or the rigid and the tender, or the male and the female, or heaven and earth, or yang and yin, or qian and kun, there are according to the Yijing two independent principles, and their interplay, governed by fixed laws, constitutes the universe. And these fixed laws are nothing else than the sixty-four trigrams (gua) as defined and explained, however enigmatically, in the Yijing proper. The practical Chinese mind , however, did not see this numerical conception of the world in its widest philosophical significance as Pythagoras did, but confined it to the vicissitudes of human affairs. Even when Confucius attempted to see a natural philosophical basis in the composition of the Yijing, he could not ignore its ethical bearings and plunged himself deeply into bold speculations. The most prominent trait of the Chinese mind is to moralize on every imaginable subject. They could not but betray this tendency even with the apparently nonsensical whole and divided strokes of the eight trigrams.