1)当表示否定或基本否定的词或词组位于句首作状语时用倒装。这类词或词组常用的有：never, nowhere, seldom, rarely, little, hardly, scarcely, barely, not until, not only, by no means, in no time, under no circumstances, under no condition, in no way, in no case, at no time, on no account等。
Never have I heard it before.
Nowhere can I find my lost watch.
Under no circumstance should a student cheat in the exam.
Not only was Churchill a statesman, but also a poet.
Note:当 “no sooner… than”和“hardly/scarcely… when/before”位于句首时用倒装。该结构表示“一…就…”，在时态上主句一般用过去完成时，when或than引导的从句用一般过去时。