| This paper uses the theories of cognitive linguistics, aims on a pair of words which semantic meanings are very similar and difficult to distinguish and discriminates them. This paper first introduces subjectivity theories and research outcomes in cognitive linguistics, and then choose"常常"and"往往"as comparative objects. We try to understand the differences between them, then could enrich the theory of practices of teaching Chinese as a second language, and open new perspectives and methods of describing and explaining synonyms of modern Chinese.The cognition linguistics thinks that grammar is semantic content combination and signify,the difference of grammar is decided from whose semanteme. Therefore this paper seeks the similarities and differences of"常常"and"往往"in grammar firstly, and then inspectes the combined relationship of the two words with verb components, adjective components, adverb components and dynamic auxiliary words, their location condition in sentences, and their selections of modal styles of sentences. By analyzing the language materials, this study found that some of researchs by predecessors are not precise and some differences of grammar, such as he ordering difference associated with some adverbs, or the difference placeing in sentences and the difference with the selection of syntactical structures.According to grammatical differences, the paper further looks for differences in the syntax of the semantic differences. We found that"常常"had the meaning of regulation, impersonalism, and character of style, the semantic single-associations refered the back and its tense did not limited; While"往往"refered regularity, contrast, heteromorphism and deduction, the semantic multi-associations referring the front."往往"could be used in the preterite, the present tense and the future, except the perfect. So this shows the two words have a lot of differences in the semantics. Moreover the main reason causing these differences are the meaning of"往往", namely contrast, heteromorphism and deduction.These main semantic features we mentioned above represent speaker′s angle, mood and cognition respectively, which make of subjectivity of"往往". In other words, the two words′differeces in grammar are caused by the subjectivity of"往往"principally. |