非真实条件句

1）时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。

a.同现在事实相反的假设。

句型 ： 条件从句 主句

一般过去时 should( would) +动词原形

If they were here, they would help you.

b.表示于过去事实相反的假设。

句型： 条件从句 主句

过去完成时 should(would) have+ 过去分词

If he had not been ill and missed many classes, he would have made greater progress.

（含义： He was ill and missed many lessons, so he did not make greater progress.）

c.表示对将来的假想

句型：条件从句 主句