Abstract: Presupposition is closely related to the clarity,accuracy,precision and depth which is required by critical thinking.If we want to analyse presupposition,we must know the ties and differences between pragmatic presupposition and semantic presupposition,and gradually analyse,also we need a good grasp of the extent to analysis,the goal is to guarantee the the clarity,accuracy,precision and depth of thinking as possible as we can,and we must be careful when we meet complex question.When we use pres..