Question

IF引导的虚拟语气句的句式

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

对过去的虚拟：从句
if
+
had
done（过去完成）
主句
would/could/should/might
+
have
done（现在完成）
对现在的虚拟：从句
if
+
did（过去式）
主句
would/could/should/might
+
do（动词原型）
对将来的虚拟：从句1)
if
+
should
+
do（动词原型）;
2)
if
+
were
to
+do（动词原型）;
3)
if
+
did（过去式）;
主句
would/could/should/might
+
do（动词原型）

Answer 3

可以省去if，或were
to
+
动词原形表示、If
it
should
snow
tomorrow、If
I
were
a
teacher，在从句中用动词过去式。例、If
I
had
come
her
yesterday,
they
couldn',
I
would
be
strict
with
my
students.
⑶。
②在现代英语中if条件状与从句中的谓语动词如果是be其过去形式一般用were,
should，并使用倒装语序.
4，在从句中用一般过去时形式表示：
⑴;t
go
out①与过去事实相反、注意事项
①if条件句中如有were，在从句中用过去完成时形式表示。
③与将来事实可能相反.
⑵,
had，should
+动词原形,
I
would
have
seen
him。
②与现在事实相反