语气
语气是动词的一种形式，它表示说话人的看法和态度。
1、陈述语气：动作或者状态是现实的、确定的或者符合事实的，具有肯定和否定形式。
例如：Physical activity does the body good, and there's growing evidence that it helps the brain too. 其中谓语动词 does。 例如：It is not the housing type, they found, that creates differences in residents' responses. 其中 it 在句子中做形式主语，that creates differences in residents' responses 是真正的主语，
2、疑问语气：用来提出问题的语气。
例如：Did you miss me? 例如：Does assisted living really mark a great improvement over a nursing home, or has the industry simply hired better interior designers?
3、祈使语气：向对方提出请求、邀请、忠告、指示、警告、命令等。谓语动词用动词原型。
例如：Hurry up! 例如：Someone call 911! 例如：Cross the street and turn left. 表示指示语气。
4、虚拟语气：所说的话只是一种与事实相反的主观愿望、假设或者是建议。
4.1）虚拟条件句
4.1.1）对现在情况的虚拟：（从句）if + v.过去式，（主句）would/should/might/cloud + v.原型
例如：If I knew it, I cloud tell you what to do. 如果我知道我会告诉你，事实上我不知道。 例如：If I were a boy, I think I would understand how it feels to love a girl.
4.1.2）对过去情况的虚拟：（从句）if + have + done，（主句）would/should/might/cloud have done。
例如：If you had told me to, I would have paid him. 如果你那么时候告诉我，我那个时候就会给钱他了，事实上没有告诉我。 例如：If I had been there, things would not have happened. 如果我那个时候在那里事情就不会发生了，事实上我不在那里并且事情已经发生了。
4.1.3）对将来的虚拟：（从句）If + should/were to do/v.过去式，（主句）would/should/might/cloud do。
例如：If I asked him, he would help us. 例如：If things all to be twice, all would be wise.
4.2）常见虚拟语气
4.2.1）would rather
对现在或者将来的虚拟，动词使用过去式
例如：I would rather you came next Saturday. 我宁愿你下周六再过来，事实上现在就过来了。
对过去虚拟，使用过去完成时 have + done
例如：I would rather you hadn't told me. 我宁愿你没有告诉过我，事实上你已经告诉我了。
4.2.2）wish/if only
对现在的虚拟
例如：I wish I were you. 我希望我是你，事实上我不是你。
对过去的虚拟
例如：I wish you had come to the party. 我希望你来了，事实上没有来。
对将来的虚拟
例如：I wish you cloud come tomorrow. 我希望你明天能够过来，有可能你后天过来或者不来。
4.2.3）表示建议、命令、要求等的动词引导的宾语从句，结构：should+v.原型。
常见动词：command、order、suggest、propose、advise、recommend、demand、require、request。
例如：John demands that I should go there at once. John要求我马上到达那里。 例如：The doctor advised that he should rest for a week. 医生建议他休息一个星期。
4.2.4）在定语从句中，表示“早该做某事”
it is high/about time + 主语 + v.过去式/should do
例如：It is high time we got up. 我们早应该起床了。 例如：It is high time you should do some exercise.