Question

if引导的虚拟语气应该用什么时态

Answer 1

1.
表示与现在事实相反的情况，其句型为“
if+
主语
+
动词的过去式（
be
动词用
were
），主语
+would
/
could
/
might
/
should
+
动词原形”。如：
If
the
weather
were
fine,
we
would
go
to
Shanghai.
如果天气好，我们就去上海。（事实上天气不好）
If
they
had
time,
they
would
/
could
/
might
go
with
me.
如果他们有时间，他们就会（可能）和我一起去。
2.
表示与过去事实相反的情况。其句型为“
if
+
主语
+
动词的过去完成式，主语
+would
/
could
/
should
/
might
+
have
+
动词的过去分词”。如：
If
I
had
taken
his
advice,
I
shouldn't
/
wouldn't
/
couldn't
have
made
such
a
mistake.
如果我按照他的建议去做，我一定不会（不可能）犯这样的错误。
3.
表示与将来事实可能相反的假设和结果，其句型为“
if
+
主语
+
动词的过去式
/
should
+
动词原形
/
were
to
+动词原形，主语
+would
/
could
/
might
/
should
+
动词原形”。如：
The
glass
would
break
if
you
dropped
it.
杯子摔下来会打破的。（事实上没有摔下来）
If
it
should
rain,
the
crops
would
/
could
/
might
be
saved.
假如天下雨，庄稼就一定（有可能）会得救。

Answer 2

1、对现在情况的假设：表示说话时不存在或与事实相反的情况.形式：If+主语+did,主语+should/
would
/could
+do.例句：If
you
knew
english
well,you
would
be
able
to
talk
with
foreigners
freely.
2、对过去情况的假设：表示与过去事实相反的情况.形式：if+主语+had
done,主语+should/would
/could+have
done.例句：if
i
had
not
studied
hard
,i
might
have
failed
in
the
exam.（事实是我通过考试了）
3、对将来情况的假设：表示将来实现可能性不大的情况.形式：if+主语+did/were
to
do
/should
do,主语+should
/would
/could
do.例句:if
he
should
change
his
mind
,what
would
we
do?