關于虛擬語氣的省略與倒裝問題

虛擬條件句的從句部分若含有were, should 或had，可省略if，再把were, should或had 移到從句的句首，使用倒裝句型。例如：

Had I known your address, I would have written before.= If I had known your address, I would have written before. 我要是知道你的地址我早就給你寫信了。

Were they here now, they could help us. =If they were here now, they could help us. 他們現在在的話，就會幫助我們了。

注：若條件從句為否定句，否定詞not應置于主語之后，而不能與were, should, had 等縮略成Weren’t, Shouldn’t, Hadn’t而置于句首。另外，有時省略if后提前的had不是助動詞。如：

Had I time, I would come. 假若我有時間，我會來的。(=If I had time…)