【问】 have to和have got to在表示“必须”这个意义时，是否可以互换?
 【答】 在表示一次性动作时，have to和have got to是可以互换的：
 1. I have (got) to be back by ten o'clock.
 我必须10点前返回来。
 2. I haven't got to work tomorrow.
 我明天不必上班。
 但是，当表示习惯性动作时，尤其是当句中含有表示经常性的副词(如always，often，sometimes等)时，则应使用have to，而不使用have got to：
 1. I don't usually have to work on Sundays.
 通常我在星期天不必工作。
 2. I often have to get up at 5.
 我常常必须五点钟起床。
 R. Quirk等人曾分析过下列两个句子的细微差别：
 “Jim's got to check the temperature every 12 hours. [1]
 Jim has to check the temperature every 12 hours. [2]
 have got to tends not to have habitual meaning，and when combined with a verb of dynamicmeaning，tends to refer to the future... Whereas [1] is likely to have the force of directive，stipulating what Jim's duties will be in the future，[2] is more likely to indicate a habitualaction['This is what Jim's present duties consist of']”(CGEL，P. 145)(“have got to一般没有“习惯性”的含义，而且，当它和具有动态意义的动词连用时，常常是指将来……句[1]可能含有指示，命令的意思，规定吉姆将来的职责，而句[2]更加
 可能是表示一种习惯性动作[这就是吉姆现在的职责了。]”
 have to与have got to的另一区别，就是后者不大用于过去时(在美国英语中没有hadgot to这个结构，即使在英国英语中也是颇为罕见的)：
 1. They didn't have to worry about money.
 他们那时不必为金钱而操心。
 2. I had to walk very fast to overtake you.
 为了赶上你，我不得不走得很快。
 最后一个区别，就是have to前可加助动词或情态动词，或者用在进行体和完成体结构中，而have got to却不能：
 1. I shall have to help him as much as I can. (Snow)
 我将不得不尽我所能去帮助他。
 2. He may have to cancel his plan.
 他也许不得不取消这个计划。
 3. People are having to boil their drinking water during this emergency. (CGEL)
 在这个紧急状况下，老百姓必须煮沸他们的饮用水。
 4. The administration has had to make unpopular decisions. (CGEL)
 行政部门不得不做出不得人心的决定。