对比原则
　　She is usually prompt for all her classes, but today she arrived in the middle of her first class。
　　but表示意思的转折，因此可以看出but前后的意思是相反的。后半句说，她今天在第一节课上了一半时才来。反推回去，她平时应该是一向“准时”的了。
　　The pain on the cottage had peeled in a few places, otherwise they looked well kept。
　　句中peel可从otherwise后面的对比猜出是“脱落”之意。

　　说明原则
　　Ann is very smart. She always knows the answers to all the teachers’questions。
　　第二句是对前一句的补充说明。一个能回答老师所有问题的女孩，Ann一定是很“聪明”的。

　　Capacitance, or the ability to store electric charge, is one of the most common characteristics of electronic circuits。
　　由后半句的解释我们很快猜出生词capacitance词义——电容量。

　　顺序原则
　　After Ms Ellis put the letters in the envelope, she sealed it and put a stamp on it。
　　在发信时，先把信装入信封，封上口，然后贴上邮票，是合理的顺序，通过前后动作，不难看出seal是“封口”的意思。

　　接下来我们再做个练习，请看下面的文段：
　　After we had travelled for about twenty miles, there was still no sign of the town which was marked on the map. We were beginning to get worried. Then, without warning, the car stopped. A quick examination showed that we had run out of petrol. Although we had little food with us, only a few biscuits and some chocolate, we decided to spend the night in the car。
　　这一段中，假设petrol和biscuit两个词是生词，但我们可以从句子的前后文中推断出这两个词的意思。如文中提到汽车在没有任何出毛病的先兆时就突然停了，文中又有run our of——“用完”这个词组，因此可以推断出一定是汽油用完了，从而petrol的意思即可推测出。下边的biscuit是生词，但这一句的前半句提到了 we had little food with us, biscuit和chocolate都是进一步补充说明是什么样的food，由此可见，这两样东西是“食品”。这时我们已经明白了大致的意思，不查词典，也不妨碍我们理解文章的意思。因此，就可以继续读下去，有时读到后面，又会发现前面出现的生词的意思在后面有了解释。（智慧校园大学）