部分倒装是指将谓语的一部分如助动词或情态倒装至主语之前。如果句中的谓语没有助动词或情态动词，则需添加助动词do, does或did，并将其置于主语之前。
句首为否定或半否定的词语，如no, not, never, seldom, little, hardly, at no time, in no way, not until 等。
Never have I seen such a performance.
Nowhere will you find the answer to this question.
Not until the child fell asleep did the mother leave the room.
当Not until引出主从复合句，主句倒装，从句不倒装。
注意： 如否定词不在句首不倒装。
I have never seen such a performance.
The mother didnt leave the room until the child fell asleep.
典型例题
1) Why cant I smoke here?
At no time___ in the meeting-room
A. is smoking permitted B. smoking is permitted
C. smoking is it permitted D. does smoking permit
答案A. 这是一个倒装问题。当否定词语置于句首以表示强调时，其句中的主谓须用倒装结构。 这些否定词包括no, little, hardly, seldom, never, not only, not until等。本题的正常语序是 Smoking is permitted in the meeting-room at no time.
2) Not until the early years of the 19th century ___ what heat is.
A. man did know B. man know C. didnt man know D. did man know
答案D. 看到Not until的句型，我们知道为一倒装句，答案在C，D 中选一个。
改写为正常语序为，Man did not know what heat is until the early years of the 19th. 现在将not提前，后面就不能再用否定了,否则意思就变了。