• Except in negatives and questions, the correct form is used to. 除在否定句和疑问句中之外，正确的形式为 used to：◆I used to go there every Saturday. 我以前每星期六都去那儿。◆I use to go there every Saturday.
• To form questions, use did. 构成疑问句用 did：◆Did she use to have long hair? 她过去留长发吗？ Note that the correct spelling is use to, not 'used to'. 注意：正确的拼写为 use to，而非 used to。
• The negative form is usually didn't use to, but in BrE this is quite informal and is not usually used in writing. 否定式通常为 didn't use to，但在英式英语中，此形式相当口语化，通常不用于书面语中。
• The negative form used not to (rather formal) and the question form used you to…? (old-fashioned, very formal) are only used in BrE, usually in writing. 否定式 used not to（相当正式）和疑问式 used you to ...?（过时且非常正式）只用于英式英语，而且通常作书面语。

• The modal verbs are can, could, may, might, must, ought to, shall, should, will and would. Dare, need, have to and used to also share some of the features of modal verbs. * can、could、may、might、must、ought to、shall、should、will 和 would 均为情态动词。dare、need、have to 和 used to 亦具有情态动词的某些特性。
• Modal verbs have only one form. They have no -ing or -ed forms and do not add -s to the 3rd person singular form. 情态动词只有一种形式，没有 -ing 或 -ed 形式，第三人称单数也不加 -s：◆He can speak three languages. 他会说三种语言。◆She will try and visit tomorrow. 她明天将设法去参观。
• Modal verbs are followed by the infinitive of another verb without to. The exceptions are ought to, have to and used to. 情态动词后跟不带 to 的动词不定式，但 ought to、have to 和 used to 例外：◆You must find a job. 你必须找到一份工作。◆You ought to stop smoking. 你应当戒烟。◆I used to smoke but I gave up two years ago. 我过去抽烟，但两年前就戒了。
• Questions are formed without do / does in the present, or did in the past. 疑问句现在时不用 do/does，过去时不用 did：◆Can I invite Mary? 我可以邀请玛丽吗？◆Should I have invited Mary? 我本该邀请玛丽吗？
• Negative sentences are formed with not or the short form -n't and do not use do / does or did. 否定句用 not 或简约式 -n't，不用 do/does 或 did。

You will find more help with how to use modal verbs at the dictionary entries for each verb. 情态动词的不同用法可参考本词典里各情态动词词条。

• Do not confuse used to do sth with be used to sth. 不要混淆 used to do sth 与 be used to sth。
• You use used to do sth to talk about something that happened regularly or was the case in the past, but is not now * used to do sth 指过去惯常做某事，而现在则不了：◆I used to smoke, but I gave up a couple of years ago. 我以前抽烟，但几年前就戒掉了。
• You use be used to sth/to doing sth to talk about something that you are familiar with so that it no longer seems new or strange to you * be used to sth/to doing sth 指习惯于、适应于：◆We're used to the noise from the traffic now. 现在我们已经适应车辆往来的噪音了。◆I'm used to getting up early. 我习惯早起。 You can also use get used to sth 亦可用 get used to sth：◆Don't worry—you'll soon get used to his sense of humour. 别担心，你不久就会适应他的幽默感。◆I didn't think I could ever get used to living in a big city after living in the country. 我觉得我在农村住了之后就无法适应大城市的生活了。