The purpose of this paper is to clarify meanings of“ social construction of knowledge” in Dewey’s learning theory as a social constructivism from the viewpoint of language. A peculiar point of view concerning language in this paper is from Keizaburo Maruyama’s interpretation of Ferdinand de Saussure’s theory. Through the consideration, two points were clarified: 1) Dewey regarded language not langue as a grammatical system but based on langage as human’s symbolization competence. It caused Dewey’s ambiguous attitudes toward language; 2) The social construction of knowledge using “language as a tool” is a construction of experience through thinking and an expansion of experience through a circle of primary and secondary experiences with language. Three practical points were suggested: 1) The means for learning should be expanded; 2) A teacher’s attitude should be changed from the subjectbased to inter-subjects; 3) Making use of language as a tool (palore) is important. It is obvious that physical activities are essential for learning and an awareness of activities using language as a tool is critically important. Teachers as well as texts as a teaching material should support learner’s awareness of the world.