情态动词全家福：
现在推测
1、肯定推测（情态动态+一般式）
he is sick 100%肯定
he must be sick 90%肯定 很有把握
he may be sick 50%肯定 不太有把握
he could/might be sick 25%肯定 很没有把握
will/should = must （will多用于将来 should见下一章,也可以用于现在）
2、否定推测
it isn't good 100%肯定
it can't/couldn't be good 90%肯定
it may not be good 50%肯定
it might not be good 25%肯定
将来推测（情态动态+一般式）
it will rain tomorrow
it should/would rain tomorrow
it may rain tomorrow
it might/could rain tomorrow
以上确信程度由高至低
would should 表示肯定程度较大的预测
may 表示约50%肯定的预测
might/could 表示25%的预测
关于should
should对说话人希望发生的事进行推断的，若将来的事情不是他所期望发生的，则不用should表示推测。
如：should be longer and more difficult than som predict. 如果小布什用should这样说，意味着他希望战争“越持久越艰难越好”
否定推测：
can't/couldn't比may not/might not否定语气强烈
过去推测（情态动词+完成式）与对现在推测相同的程度：
he must have been sick
he may have been sick
he could/might have been sick
也可用can will should would
can't/couldn't比may not/might not否定语气强烈
推测用法四（情态动词+（完成）进行时）
用法同以上~
