摘要：
The positive-negative contrasts containing affirmation and negation embody the differentiation of the things and the intention of the speakers. So the positive-negative contrasts can be used to make differentiation and interpretation. The author approaches the subject from the following three angles： the patterns and properties, the focus, the main emphasis and the intensity. There are two patterns ofXian Li Hou Po（先立后破） and Xian Po Hou Li（先破后立） in the positive-negative contrasts, and the latter is the commonly used one. The property of the positive-negative contrasts is semantic or pragmatic. The contrastive focus is located at the ahead, the behind or the ahead-behind. The symmetry of the patterns depends on the location of the focus. The contrastive focus is single or double. The content of the focus is related to the location of the focus and the meaning of the clause of Shi（是）. We can lay stress on the focus in the devices of elision, implication or sharing, and also enrich the contents of the focus through expanding, attaching or various-corresponding focus. The focus is static or dynamic. The main emphasis of the positive-negative contrasts lies on the positive clause of Shi（是）. The scale of intensity of the positive-negative contrasts divides into the strong, the moderate, the weak and the compound, among them the moderate intensity is the basic one.
