• Should and ought to are both used to say that something is the best thing or the right thing to do, but should is much more common. * should 和 ought to 均用以表示应该做某事，不过 should 常用得多：◆You should take the baby to the doctor's. 你应该把这婴儿带去看看医生。◆I ought to give up smoking. 我应该戒烟。 In questions, should is usually used instead of ought to. 在疑问句中，通常用 should 而不是 ought to：◆Should we call the doctor? 我们叫医生来好吗？
• Had better can also be used to say what is the best thing to do in a situation that is happening now. * had better 亦可用以表示在目前状况下最好做某事：◆We'd better hurry or we'll miss the train. 我们最好快点，否则就赶不上火车了。
• You form the past by using should have or ought to have. 过去时用 should have 或 ought to have 构成：◆She should have asked for some help. 她本应该请求帮助的。◆You ought to have been more careful. 你本应该更小心一点的。
• The forms should not or shouldn't (and ought not to or oughtn't to, which are rare in NAmE and formal in BrE) are used to say that something is a bad idea or the wrong thing to do. * should not 或 shouldn't（以及在美式英语中很少见，在英式英语中为正式用法的 ought not to 或 oughtn't to）表示不应该：◆You shouldn't drive so fast. 你不应该把车开得这么快。
• The forms should not have or shouldn't have and, much less frequently, ought not to have or oughtn't to have are used to talk about the past. * should not have 或 shouldn't have 以及很少用的 ought not to have 或 oughtn't to have 均用于指过去：◆I'm sorry, I shouldn't have lost my temper. 对不起，我不该发脾气。

• In modern English, the traditional difference between should and would in reported sentences, conditions, requests, etc. has disappeared and should is not used very much at all. In spoken English the short form 'd is usually used. 在现代英语中，should 和 would 在间接引述中、在表示条件、请求等句子中的传统区别已不复存在；should 基本上不怎么用。在口语中常用简约式 'd 表示：◆I said I'd (I would) be late. 我说我要迟到了。◆He'd (he would) have liked to have been an actor. 他本来想当演员。◆I'd (I would) really prefer tea. 我倒是更喜欢喝茶。
• The main use of should now is to tell somebody what they ought to do, to give advice, or to add emphasis. 现在 should 主要用于告诉某人应该做什么、给予忠告或加强语气：◆We should really go and visit them soon. 我们的确应该马上去看看他们。◆You should have seen it! 你应该看见的！

• 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。