Question

can't/couldn't have的意思

can't/couldn't have done的意思是 本来不可能做某事结果做了 还是 表示过去动作不可能发生？这两者又有什么区别呢

Answer 1

can
have
donecan
have
done
通常只用于否定句和疑问句。用于否定句时表否定推断，推测肯定没做；用于疑问句时意为“难道真的做了吗”，表示怀疑。例如：Can
he
have
done
such
a
foolish
thing?
(=
Is
it
possible
…?)
他会做这样的傻事吗？（表怀疑）He
can't
have
taken
it
home.
他不可能把它带回家了。（表不可能）could
have
donecould
have
done
可用于肯定句、疑问句和否定句。用于肯定句既可以表示过去能够做而实际未做，有惋惜、遗憾或委婉批评之意，也可以表示对过去动作的推测；用于否定句和疑问句的情况与can
have
done相同。例如：You
could
have
done
better,
but
you
didn't
try
your
best.
你本可以做得更好，但是你没有尽力而为。（表惋惜）This
glass
is
cracked.
Someone
could
have
dropped
it.
这个玻璃杯破了。可能是谁把它掉在地上了。（表推测过去）Could
he
have
left
the
work
unfinished?
他会丢下工作不干了？（表怀疑）He
couldn't
have
checked
out
so
early.
他不可能这么早就离开了。（表不可能）注意：can't
have
done
的语气比
couldn't
have
done
要强一些。例如：He
can't
have
been
to
that
town.
他根本不可能去过那座城市。（语气略强）The
measurement
couldn't
have
been
wrong.
测量不可能出错了吧。（语气稍弱）