在大学英语四六级中，单独考察的题几乎没有，但是语法知识点却贯穿整张试卷，下面是小编为大家整理的知识，希望可以为大家带来帮助，一起来学习一下吧。

非真实条件句

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

Iftheywerehere,theywouldhelpyou.

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

Ifshehadworkedharder,shewouldhavesucceeded.

Thericewouldnothavebeenburntifyouhadbeenmorecareful.

IfmylawyerhadbeenherelastSaturday,hewouldhavepreventedmefromgoing.

Ifhehadcomeyesterday,Ishould/wouldhavetoldhimaboutit.

含义：Hedidnotcomeyesterday,soIdidnottellhimaboutit.

Ifhehadnotbeenillandmissedmanyclasses,hewouldhavemadegreaterprogress.

含义：Hewasillandmissedmanylessons,sohedidnotmakegreaterprogress.

c.表示对将来的假想

句型：条件从句

主句

一般过去时

should动词原形

were不定式

would动词原形

should动词原形

Ifyousucceeded,everythingwouldbeallright.

Ifyoushouldsucceed,everythingwouldbeallright.

Ifyouweretosucceed,everythingwouldbeallright.