Putting forward 'Theory of Middle Term' as social studies class based on 'theory of thought reciprocation' and 'theory of knowledge growth', Katakami Sougy criticizes that conventional problem-solving type social studies class is composed of theory of knowledge acquisition and theory of one way of thinking, so it does not grow knowledge. He points out the problem of problem solving type class method based on Dewey's five-phase theory as source of theory of one way of thinking in theory of thought reciprocation, and the problem that it is difficult for acquisition type theory of knowledge based on problem-solving type class method to acknowledge the growth process of knowledge in theory of knowledge growth. For this reason, he insists a question-oriented type or an object-accepting type, not a problem-solving type. Here it directs for a reciprocation type thought, not an one-way type thought, a growth-type knowledge, not an acquisition type knowledge and an open-type class leaving furthered question, not a closed type class not leaving questions. Katajami Sougy's theory of class expands the viewpoint and horizon of social studies class in that it puts value on children's independent pursuit activity and knowledge growth in composing class and is wary of that children's thought or knowledge is fixed.