have to

have to加动词原形

表示不得不、必须的概念。它比must更含有客观条件使得必须如此做的意思，并有较多的时态。如：

Mr. Johnson has to work very hard to earn a living.约翰逊先生为了谋生不得不拼命干活。

I had to leave the party early last night. I wasn't very well.昨晚我只得早点离开晚会，我不大舒服。

We will have to get up very early tomorrow.我们明天必须起得很早。

I shall have to go to the clinic today for my bad cough.我咳嗽得厉害，今天必须去诊疗所看看。

[注]口语中的I have got to，you have got to等：I have to，you have to. Have I got to?和Do I have to?这两种疑问形式均可用。

[英语语法手册]情态动词--shall

shall

shall作为情态动词用于第二、三人称

可表示说话人给对方的命令、警告、允诺、威胁等概念。如：

You shall do it，whether you want to or not. 不管你愿意不愿意，你必须做这项工作。(命令)

You shall have the book as soon as I finish it.这本书我一看完就给你。(允诺)

You shall pay for it.你一定会受到惩罚的。(威胁)

在疑问句中，情态动词shall用于第一、三人称

表示说话人征求对方的意见或向对方请示。如：

What shall I do now? 我现在该做什么?

Shall we go for a walk? 我们去散步好吗?

Shall he come tomorrow? 你要他明天来吗?