have to可视为实义动词（有正常的人称、数、时态、语态、否定、疑问等用法），也可以表达为have got to，但是，have got to仅仅相当于一个情态动词用法。have to有以下几种用法：
1. 含义：必须；不得不(表示外在或客观的原因必须，不得不做什么事) 如规定、法律和他人的愿望
这个时候，相当于一个实义动词：
Did she have to pay a fine?
她非得交罚款吗？
I felt sure I'd have to kiss my dancing career goodbye.
我明确感觉到我将不得不与我的舞蹈生涯说再见了。（kiss多么生动、地道、形象的表达啊）
You don't have to knock─just walk in.
不必敲门——进来就是了。
I have to collect the children from school at 3 o’clock.
我得在3点钟到学校接孩子。
Nurses have to wear a uniform.
护士必须穿制服。
I have to finish this essay today. We have to hand them in tomorrow.
我今天得完成这篇论文，因为我们明天必须交。
The weather will be the biggest hurdle so I have to be ready.
天气将会是最大的障碍，所以我必须要作好准备。
We’ll have to borrow the money we need.
我们需要的这笔钱只好去借了。
I enumerate the work that will have to be done.
我列举了必须得做的一些工作。
带有have to的疑问句由do构成：
Do the children have to wear a uniform?
孩子们必须穿制服吗？
I have to leave. Nice to have met you.
我得走了。认识您很高兴。
I'll have to fly.
我得赶紧走了。
Do you have to go?
你非得走吗？
Have you got to go?
你非得走吗？
其否定形式表示没有必要做某事用don't have to：
You don’t have to pay for the tickets in advance.
你不必预付票款。
She doesn’t have to work at weekends.
她周末不用上班。
Credit cards can be handy — they mean you do not have to carry large sums of cash.
信用卡很方便，有了它你就不用携带大量现金了。
2.表示一定真实或肯定发生：一定，必将
There has to be a reason for his strange behaviour.
他的古怪行为一定事出有因。
This war has got to end soon.
这场战争必将很快结束。
3. 劝告或建议时用
You simply have to get a new job.
你就是得找份新工作。
You've got to try this recipe─it's delicious.
你得试试这种烹调法——味道很不错。
4. 用以暗示麻烦的事或某人有意捣蛋
Of course, it had to start raining as soon as we got to the beach.
可恶的雨，我们一到海滩它就非得下起来。
Do you have to hum so loudly? (= it is annoying)
你非得用这么大嗓门哼唱不可吗？
最后这种用法的时候have to不可以换成have got to。
5. have to可以与may等情态动词连用，如：
I think you may have to finish the work today.
我想你今天(也许)得完成这项工作。
If the cortisone doesn't take, I may have to have surgery.
如果可的松无效，我恐怕只能动手术了。
As a last resort you may have to accept their point of view.
最终，你可能不得不接受他们的观点。
You may have to learn a few new skills along the way.
在这个过程中你可能还得新学几招。
Hungary may have to lower its hopes of shrinking its state sector.
匈牙利可能不得不降低其缩小国家军事管制区的期望。
His tour may have to be cancelled altogether
他的旅行可能不得不彻底取消。
The sufferer may have to make major changes in his or her life to arrest the disease
患者可能必须对生活习惯作出重大调整以控制病情。
He may have to become more conformist if he is to prosper again
要想再现辉煌，他可能得更多地依照习惯办事。
Learners may have to take a written exam before they pass their driving test
学员在通过驾照考试前可能得参加笔试。
《柯林斯高阶英汉双解学习词典》
I may have to ask for your advice later on.
以后少不得要去向您讨教。
This office's resources and staff would have to be increased to cope
with the extra workload.
要应付额外的工作，必须增加这个办公室的资源和人手。
He would have to accept it; there was no other way
对此他将别无选择，只有接受。
You would have to be pretty hard-hearted not to feel something for him.
只有铁石心肠的人才会对他无动于衷。
If they wanted a deal at any price, they would have to face the consequences
如果他们无论如何都想达成交易，他们就得承担其后果。
If someone tried to bash my best mate they would have to bash me as well
如果谁想揍我最好的朋友，那我就跟他拼了。
I would have to learn, little by little, to exist alone.
我得慢慢学会独自生活。
No American should have to drive out of town to breathe clean air
所有美国人都不必开车到城外去呼吸洁净的空气。
He would not be unhappy though he should have to live alone.
虽然他不得不要一个人住，却没有不开心。
