if的用法总结

if的用法：表示条件，意思是如果；表示虚拟，意思是假如；表示是否的含义，和whether相同用法，连接宾语从句。

1.(表示条件)如果,主句用将来时,if从句用现在时表示将来

Hewillcomeifyouinvitehim.

如果你请他,他会来的.

2.(表示虚拟)假如,要是

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.

3.是否=whether连接宾语从句

Iwonderifsheisill.

不知她是否病了.