This paper presents the principle of symbol grounding in robots. If a robot does not understand words, the robot cannot autonomously talk in the physical world. Understanding language symbols is a necessary condition for autonomous conversations. First, how humans understand language symbols is briefly studied. Humans’ symbol manipulation is based on imagination. Recent brain science shows that imagination is a virtual bodily movement. Therefore, humans’ symbol manipulations are based on virtual bodily movements. Based on virtual bodily movements, a principle of symbol manipulation (grounding) in robots is presented. The idea called Embodied AI. The semantics is called the embodied semantics, and the architecture is called the embodied architecture. In the embodied AI, abstract symbols are grounded through metaphors.