if用什么時態？

用現在時表示將來

He will come if you invite him.

如果你請他,他會來的.

2.(表示虛擬)假如,要是

時態：可以表示過去,現在和將來的'情況.它的基本特點是時態退后.

a.同現在事實相反的假設.

句型 ：條件從句 主句

一般過去時 should( would) +動詞原形

If they were here,they would help you.

b.表示于過去事實相反的假設.

句型：條件從句 主句

過去完成時 should(would) have+ 過去分詞

If she had worked harder,she would have succeeded.