如何判断一个使用虚拟语气的句子表示的是现在的事还是过去的事？

1.if结构（非真实条件句——表示的是假设的或实际可能性不大的情况）
与..事实相反
If从句
主句
过去
Had
done
Would*
have
done
现在Were/did
Would*
do
将来Should
do/were/were
to
do
Would*
do
例句：If
there
hadn’t
been
much
rain
in
spring,
we
would
have
had
a
good
harvest
now.
【过去】
If
he
smoked
less,
his
cough
might
be
well
soon.
【现在】
If
the
lecturer
should
be
late,
you
would
have
to
make
a
speech
first.
【将来】
备注：
（1）上表中’*’，would都可转换为should、could、might。
（2)
如果为时间错综句的话，左右两栏可互相搭配，排列组合。
例句：
He
would
still
be
alive
today
if
he
hadn’t
taken
that
drug.
【与现在事实相反】
【与过去事实相反】
(3)
if可转换为其他形式
例句：Without
your
advice,
our
meeting
wouldn’t
have
been
so
successfully.
【过去】
（=>可转换为：If
there
hadn’t
been
your
advice,
we
…）
Your
notes
are
almost
illegible
(难以辨认的).
Notes
typed
out
would
be
a
lot
easier
to
read.
【将来】
(=>
可转换为：If
the
notes
had
been
typed
out,
it
would
be
a
lot
easier
to
read.)
I
should
have
gone
to
see
Dr.
Smith
and
he
might
have
cured
me
of
the
disease.【过去】
(=>
可转换为：If
he
have
gone
to
see
Dr.
Smith,
he
..)

虚拟语气概念
　　　虚拟语气用来表示说话人的主观愿望或假想，所说的是一个条件，不一定是事实，或与事实相反
在条件句中的应用
　　条件句可分为两类，一类为真实条件句，一类为非真实条件句。非真实条件句表示的是假设的或实际可能性不大的情况，故采用虚拟语气。
真实条件状语从句与非真实条件状语从句
　　eg
.
　　if
he
doesn’t
hurry
up,
he
will
miss
the
bus.
(
真实条件状语)（不是虚拟语气）
　　if
he
was
free,
he
would
ask
me
to
tell
stories.
（真实条件状语）（不是虚拟语气）
　　if
i
were
you,
i
would
go
at
once.
（非真实条件状语从句）
　　if
there
were
no
air,
people
would
die.
（非真实条件状语从句）
　　总结：主将从现，主句用将来时，从句用一般现在时。
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