主要区别如下：
1.
用于
疑问句表示请求时，一般只用Could,且可用于各人称。如：
Could
you
help
me
explain
the
difference
between
"might"
and
"could"?
Could
I
use
your
mobile
phone
a
little
while?
上句可用May代替：May
I
use
your
mobile
phone
a
little
while?
用Might也是可以的，但不常见。
2.
could和might都可用在条件句中，表示假想的情况。表示“本来会、本来可以/能够”。例如：
If
you
tried
you
could/might
do
the
work
better.
如果你试试的话，准能把那项工作干得更好。
You
could
have
met
her
if
you
had
gone
that
way.
如果你走那条路的话，你准能遇见她。
此句中的could如改成might则表示：……，你也许能见到他。
They
could/might
have
worked
it
out
if
they
had
asked
me
for
help.
如果他们来向我求助的话，他们本能够做出来的。
He
could/might
have
give
the
answer,
but
he
refused
to.
他本来能够回答的，但他拒绝这么做。
You
were
stupid
to
go
skiing
there
—
you
could
have
broken
your
leg.
你真笨，竟会到那地方滑雪。你本来会摔断腿的。
上面的例句中用might则因其语气较轻而语意效果不甚理想。
在此场合，could和might的区别是could较might的可能性强。
3.
couldn't
be
+
比较级句型不能用might代替。如：
Their
lifestyles
couldn't
be
more
different.
他们的生活方式极为不同。
4.
could和might都可用在表示“结果”的
状语从句中，同样，could语气较重些。例如：
He
expressed
his
ideas
clearly
so
that
the
average
person
might
understand.
他把他的意思清楚地表达出来，以便一般人能听明白。
5.
might
as
well表示“不妨、可以、倒不如”，此时的might是不能用could代替的。例如：
We
might
as
well
look
for
some
food
now.
现在我们不妨找些吃的东西。
I
expect
I
might
as
well
be
going.
我希望我可以走了。
Since
it’s
a
fine
day
we
might
as
well
walk.
既然是一个晴朗的天，我们不妨步行。
We
might
as
well
have
gone
home
as
you
suggested.
我们还不如按你建议的回家去呢。