【倒装的条件】
　　当only修饰状语且“only 状语”的结构位于句首时，后面的句子需要倒装。
　　这里的状语可以是副词、介词短语或状语从句。
　　如果only修饰的不是状语，句子就不能倒装。比如Only some of the students passed the examination一句中，only修饰的是主语some of the students，所以句子不能倒装。若把它写成Only some of the students did pass the examination，就错了。
　　即使only修饰的是状语，但若“only 状语”的结构不位于句首，句子也不能倒装。比如Peace and equality were made possible only after a bitter struggle一句，就不能倒装。
　　【倒装的方法】
　　only修饰状语且位于句首时，须把主句谓语中的助动词或情态动词提至主句的主语之前，形成倒装。
　　如果主句谓语中没有助动词或情态动词，则要根据时态添加助动词do， does或did，再将它置于主句的主语之前。
　　比如Our honor can be saved only in this way一句，如果把only in this way置于句首，形成倒装，只需把主句谓语中的情态动词can提至主句的主语our honor之前。倒装后的句子为：Only in this way can our honor be saved.
　　又比如He realized that he was wrong only then一句，如果把only then置于句首，形成倒装，由于主句谓语realized不含助动词或情态动词，所以应根据时态添加did，再将其置于主句主语he之前。倒装后的句子为：Only then did he realize that he was wrong.
　　要注意的是，only修饰的是状语从句时，千万不要错把这个状语从句谓语中的助动词或情态动词也提前了，也不要错把句中其他从句谓语中的助动词或情态动词提前。
　　比如Only when we had studied the data again did we realize that there was a mistake一句，only修饰状语从句when we had studied the data again且置于句首，因此主句要倒装；又因为主句中没有情态动词或助动词，所以根据时态添加did，将其倒装于主句的主语we前。如果把when we had studied the data again这个状语从句也倒装了，写成Only when did we have studied the data again did we realize that there was a mistake；或者错把that there was a mistake这个表语从句倒装了，写成Only when we had studied the data again did we realize that did there be a mistake，纯属多此一举，弄巧成拙。