A philosophy professor warned the class he was going to give them a test. When the day came he entered the classroom, wordlessly placed his chair on the table and, turning to the blackboard, wrote, "Prove to me this chair does not exist." Most of the nervous students began intently scribbling out long dissertations. But one member of the class wrote down just two words, and then handed his paper to the teacher. The professor had to smile when he read the student's answer: "What chair?"

　　一位哲学教授通知学生他要举行一场考试。考试那天，他走进教室，一言不发地把自己的椅子放到讲台上，然后转身在黑板上写道，“请向我证明这张椅子不存在。”大多数学生很紧张，都开始专心地写他们的论文。只有一个学生只写了两个单词就交卷了。当教授看到这个学生的答案时，不由微笑了，只见他写的是：“什么椅子啊？”