• Can and cannot (or can't) are the most common words used for asking for, giving or refusing permission. * can 和 cannot（或 can't）是表示请求、给予或拒绝许可的最通用词：◆Can I borrow your calculator? 我可以借用你的计算器吗？◆You can come with us if you want to. 如果你愿意可以跟我们一起来。◆You can't park your car there. 你不能在那儿停车。
• May (negative may not) is used as a polite and fairly formal way to ask for or give permission. * may（否定式 may not）用以表示礼貌的正式请求或给予许可：◆May I borrow your newspaper? 把你的报纸借我看行吗？◆You may come if you wish. 你想来的话可以来。 It is often used in official signs and rules. 该词常用于正式标志和规定：◆Visitors may use the swimming pool between 7 a.m. and 7 p.m. 访客从早 7:00 到晚 7:00 可在游泳池游泳。◆Students may not use the college car park. 学生不得在学院停车场停车。 The form mayn't is hardly ever used in modern English. 现代英语几乎不用 mayn't。

• 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。