To obtain knowledge also related to the method. To obtain the right knowledge, one must take right method. Removing obstructions will be discussed first.
Removing obstructions was firstly mentioned by Chuang Tzu. In Pre-Qin Time, there were One Hundred Schools of Thought, which viewed themselves right and other wrong. Chuang Tzu said,
The country suffers disturbance. The sages have not appeared and morality differs among citizens. Some are complacent with their partial knowledge. Ear, eye, nose, and mouth have their function but cannot coordinate. Similarly, philosophers specialize in one filed but cannot know all. (Chuang Tzu, All under Heaven)
To Chuang Tzu, the schools of thought expressed reasonable views but discovered partial truth. If they considered they had learnt all the truth and they were right and others wrong, this meant dogmatism or Qu in Chuang Tzu's term. What caused dogmatism? Chuang Tzu ascribed it to the partial understanding of knowledge. Chuang Tzu exemplified,
One cannot talk about sea with a frog in well as it is limited by the environment. One cannot talk about ice with a summer insect as it is limited by the season. One cannot talk about Tao with a man in countryside as it is limited by education. (Qiu Shut")
Here, Chuang Tzu viewed the frog in well, insect in summer, and man in countryside as the representative of one-sided thinking. From the fact that dogmatism was prevalent in Chinese society and history, Chuang Tzu's thought was valuable.
Later, Xun Zi expressed insightful view on removing obstructions. In Removing Obstructions, Xun Zi proposed the idea in the beginning: "Man's common fault is one is limited by partial knowledge and unconscious of complete truth." It was notable that Xun Zi inherited and extended Chuang Tzu's thought. Xun Zi said, "What will cause obstructions? Desire, hate, seeing the start only, seeing the end only, seeing the far only, seeing the near only, profound knowledge, superficial knowledge, knowing the past only, and knowing the present only." In short, "There is difference among the objects in the world, which formed obstructions. This is the common fault in man's knowledge." Xun Zi also criticized the obstruction or one-sidedness: "Mo Zi values practice but neglects theory; Song Zi values desire but neglects the way; Shen Zi values situation but neglects knowledge; Hui Zi values language but neglects practice; Chuang Tzu values Tao but neglects human." Then, how could one avoid the one-sidedness? Xun Zi said, "The sage realizes the harm of one-sidedness and obstruction in thinking, so he dislikes neither one thing nor another, overstates neither the start nor the end, stresses neither the near nor the far, overstates neither the profundity nor the superficialness, and stresses neither the past nor the present." The core idea was to "list both sides and make a criterion," meaning the all-sidedness of knowledge.