当虚拟条件句的谓语动词含有were,should,had时,if可以省略,这时条件从句
要用倒装语序,即把were,should,had等词置于句首,这种多用于书面语.
eg：
Should he agree to go there,we would send him there.
要是他答应去的话,我们就派他去.
Were she here,she would agree with us.
如果她在这儿的话,她会同意我们的.
① 若条件从句为否定句,否定词not应置于主语之后,而不能与were,should,had 等缩略成Weren’t,Shouldn’t,Hadn’t而置于句首.
② 有时省略if后提前的had不是助动词：
Had I time,I would come. 假若我有时间,我会来的.(=If I had time…)
如果不是你救了我,我早就死掉了.
Had you not saved me,I would have been dead