In Song and Ming dynasties, the view on knowledge and action developed in a more fully and profound way. Zhu Xi was the representative in Song Dynasty. He views could be summarized in two ways.
Firstly, knowledge and action depended on each other. While commenting on the line in Doctrine of the Mean, Zhu Xi reduced into knowledge and action the line "A gentleman should study extensively, inquire prudently, think carefully, distinguish clearly, and practice earnestly." He said, "One studies, inquires, thinks, and distinguishes, so he can choose the good to learn. If one practices earnestly, he can always practice benevolence." (Commentaries to Selected Doctrine of the Mean) Here, Zhu Xi meant that what one studies, inquires, thinks, and distinguishes related to knowledge, while what one practices related to the appliance of knowledge. Then, Zhu Xi viewed that knowledge and action were interdependent. He noted, "Knowledge and action must rely on each other, like eye and foot. Without foot, one cannot move; without foot, one cannot see." (Words of Zhu Zi, Vol. 9) He also stressed that: "Neither knowledge nor action should be overstated; otherwise, both will be harmed." (Words of Zhu Zi, Vol. 9) and "When knowledge is clear, action will be well done, vice versa." (Words of Zhu Zi, Vol. 14) Evidently, Zhu Xi's view embodied the dialectic relationship between knowledge and action.
Secondly, knowledge appeared first and action was more important. Zhu Xi said, "Knowledge appeared earlier than action while action was more important than knowledge." (Words of Zhu Zi, Vol. 9) Why did knowledge appear earlier? Zhu Xi explained as follows:
With knowledge, one can cultivate himself.
How could one act if he has not obtained knowledge?
To a walking man, how could he walk if he cannot see? (Words of Zhu Zi, Vol. 9)
In contrast, Zhu Xi considered that: "One cannot act if he does not have knowledge and can act if he has." (Works of Zhu Wen Gong, Vo. 41) Why was action more important? To Zhu Xi, it was action rather than knowledge that was the purpose. Zhu Xi said, "A sage firstly teaches knowledge, but he takes action as the final purpose." (Works of Zhu Wen Gong, Vo. 54) In addition, Zhu Xi observed that action tested whether one understood the knowledge or not: "One has not obtained the knowledge if he cannot use it. This kind of knowledge is not real. There is no real knowledge that cannot be used." (Works of Zhu Wen Gong,
Vo. 72) It was noticeable that Zhu Xi mainly referred to the moral knowledge or action. Zhu Xi's view was reasonable to some extent, as for children, they should learn or study first, and then apply the knowledge. Meanwhile, there was flaw in his view. Zhu Xi confined to the moral issue and failed to note the priority of action in more fields.