Abstract: Separable words can epitomize the unique characteristics of Chinese, such as: (i) the blurred boundary between characters, morphemes, words and phrases, (ii) the cross-boundary between nouns and verbs, and (iii) the discreteness, chunkiness and reversibility of syntactic structures.Based on Humboldt's idea that there is commensurability between language and thought, and on the analysis of the structural features of Chinese characters and the relations between nouns and verbs, this paper reaches the conclusion that Chinese clearly has the trait of spatiality, which can be considered to be the essential cause of the unique characteristics of Chinese including the existence of separable words.