There are two main channels for people to learn knowledge –from books and from experience.提出两种情况 Generally, knowledge gained from books is theoretical, that gained from experience is practical. It is difficult to answer which is more important to we people. It depends on the phases and events of our learning. Knowledge learned from books is instructive教育性的, which perhaps cannot learn directly from experience. We often hear thunders雷声 and see lightning in the sky, and we can easily find that lightning will be seen sooner than sound will be heard. According to our experience alone, we cannot tell why it had happened. But when we learn some physics in textbooks, we will find the answer clearly that because light travels faster than sound does, it takes less time for light to travel the same distance than for sound. Therefore, book knowledge can inform us some useful theories that can give us general ideas and help us understand the real phenomenon better.书本知识有时比实践知识更instructive，例子举得很好 In turn反之, practice knowledge check out the theories gained from books. There is an old Chinese saying that practice is the only criterion of inspecting the truth. So not all knowledge from books is credible, even false. When Aristotle wrote in his transcripts that the earth is the center of our planets, no one doubts this for centuries. However, when Galileo read about it, he did not suspect it at first, but when he made some observation and research, he found it is not the truth. Then comes the new theory—Sun center theory.实践检验书本知识，又是一个好例子