The meaning of expression is a concept activated in the brain of the speaker or listener. More specifically, meaning lies in human's interpretation of the world, which is subjective, embodies the idea of taking human as the center of the universe, and reflects the dominant cultural connotation, the mode of communication of a particular culture and the characteristics of the world. This principle shows that the description of meaning involves the relationship between words and the brain, rather than the direct relationship between words and the world.

Words and larger language units are the entrance to the infinite knowledge network. In order to fully explain the meaning of a language expression, we usually need to consider images (visual and non-visual), metaphors, mental models and simple understanding of the world. Therefore, the meaning of a word can not be solved by an isolated dictionary definition, and it must rely on encyclopedic knowledge to achieve its goal.