Abstract: Theoretically, every language unit at different levels is a structure of the inner-outer mode, that is to say, it is a “structural-functional” entity composed by one core constituent and one or multiple outer-layer constituents. In such an inner-outer mode the location of a constituent is in direct proportion to the importance of its loaded information. To those constituents close to the inner layer, their loaded information is quite major, while to those close to the outer layer, their information is minor. As to those middle-layer constituents, their loaded information is just between major and minor in importance. Structuralistic linguistics and the theory of generative grammar pay attention to the layer character of phrases in a sentence, ignoring or throwing away other sentence layers. Discourse linguistics is concerned about sentence from the outside, while functionalistic linguistics stresses a functional analysis of sentence. Based on an assimilation of their advantages, the hypothesis about the inner-outer mode of language unit will be important to a better recognition, description and explanation of language units at different layers in theory and in practice.

Key words: language unit, inner-outer mode, inner layer, middle layer, outer layer