if引导的虚拟语气的用法

Answer 1

1.
当if后面接一般现在时的动词时,表示对将来的一种推测.
if
sb
do
sth
sb
will/shall
do
sth.
if
you
go
with
me,
you
shall
be
rewarded.
2.
当if后面接一般过去时的动词时,则是一种虚拟语气.
if
sb
did
sth
sb
would/should
do
sth.
if
i
didn't
make
that
mistake,
i
would't
have
suffered
such
a
failure.
3.
当if后面接什么时态都可以时，if为“是否”的意思，句子为宾语从句.
sb
do
sth
if
sb
do
sth.
he
said
if
rain
was
stop.
由if引导的条件状语从句，时态应该是主将从现，就是说主句用一般将来时，而从句用一般现在时表示将来。
例如
if
it
doesn't
rain
tomorrow,
i
will
visit
my
former
school.
这里从句就用一般现在时。
当然if引导的从句也可以用虚拟语气
例如if
i
got
up
early
in
the
morning,
i
wouldn't
miss
the
train.

Answer 2