Dewey's thought gradually appeared in the process of the dissolution of dualism. In the process of ending grand realism, Dewey, built up the theory of practical realism and initiated the "learning by doing" theory and inquiry pedagogical theories and promoted the democracy and reality of education through the analysis of modern science and the phenomenon of children's touching flame. But Dewey had not fully aware that knowledge learning is not a completely equivalent to such a process, it needs to be supported by hermeneutics and learning theories and other related theories. This weakness led to certain deviation of Dewey's theory. He replaced "understanding" and "learning" by "knowing" and "cognition", therefore his criticisms of Herbart is not sufficient and reasonable.