命题是学术上的一个名称，不为数学所独有，凡属于判断真假的句子都是命题．命题的第一个特征是具有判断．例1下列各语句中，哪些是命题，哪些不是命题？（1）如果两个角是对项角，那么它们相等；（2）水是无色透明的；（3）－8比0小吗？（4）作一条线段等于已知线段．解（1） The proposition is a name in the academic field. It is not unique to mathematics. Every sentence that is true or false is a proposition. The first feature of a proposition is judgment. Example 1 Which of the following statements are propositions and which are not propositions? (1) If the two corners are opposite corners, then they are equal; (2) Water is colorless and transparent; (3) -8 is less than 0? (4) Make a line segment equal to the known line segment. Solution (1)