将谓语中的助动词或情态动词置于主语之前，就是部分倒装。部分倒装通常出现在以下场合：
1. 陈述句变为疑问句时，主语和谓语要部分倒装。例如：
They are talking about the new film. Are they talking about the new film？
They are talking about the new film. What are they doing？
2. only ＋ 状语 / 状语从句位于句首时，句子的主语或主句中的主语和谓语要部分倒装。例如：
Only yesterday afternoon did I finish my experiment.
Only in this way can you catch up with your classmates.
Only when you get to the top of the mountain can you see the tower.
3. 表示否定意义的副词或连词放在句首时，主语和谓语要部分倒装。例如：
Never shall I do the same thing again.
Not until all the fish died in the river did the villagers realize how serious the pollution was.