Auxiliary verbs are helping verbs that work with a main verb to build meaning. They can show time, aspect, possibility, obligation, permission, and emphasis. In English, auxiliaries also help form questions and negatives without changing the main verb. The main auxiliary groups are be, have, do, and the modal auxiliaries.

Be is an auxiliary when it combines with another verb form. It is used to form continuous tenses with the -ing form, and passive voice with the past participle. Be changes form to match the subject and time, while the main verb stays in the needed form.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Be + -ing forms the continuous aspect	🧠 Be + -ing 形式构成进行时态	She is studying now.	🧠 她现在正在学习。
Be + past participle forms the passive voice	🧠 Be + past participle 构成被动语态	The window was broken.	🧠 窗户被打破了。
The form of be agrees with the subject and tense	🧠 Be 的形式要与主语和时态一致	They are working today.	🧠 他们今天正在工作。

Have is an auxiliary when it forms perfect tenses with a past participle. Perfect aspect connects a time to a result or experience, often showing something completed before another time. Have changes form for the subject and tense, while the main verb uses the past participle.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Have + past participle forms the perfect aspect	🧠 Have + past participle 构成完成体	I have finished my work.	🧠 我已经完成了我的工作。
Had marks the past perfect for an earlier past time	🧠 Had 表示更早时间的过去完成时	She had left before noon.	🧠 她在中午之前离开了。
Perfect aspect can express experience up to now	🧠 完成体可以表达至今的经历	They have visited Paris.	🧠 他们曾经去过巴黎。

Do is an auxiliary used to form negatives and questions in simple present and simple past when there is no other auxiliary. It also appears in short answers and can add emphasis in affirmative statements. When do is auxiliary, the main verb stays in the base form.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Use do to make negatives in simple present or past	🧠 使用 do 构成一般现在时或过去时的否定句	He does not like coffee.	🧠 他不喜欢咖啡。
Use do to make questions in simple present or past	🧠 使用 do 构成一般现在时或过去时的疑问句	Do you work here?	🧠 你在这里工作吗？
Use do for emphasis in affirmative statements	🧠 在肯定句中用于强调时使用 do	I do want to help.	🧠 我确实想帮助。
After do, the main verb stays in the base form	🧠 使用 do 之后，主谓动词保持原形	She did not go yesterday.	🧠 她昨天没有去。

Modal auxiliaries add meanings like ability, possibility, permission, advice, and obligation. Common modals include can, could, may, might, must, shall, should, will, would, and ought to. Modals do not take -s, do not use do-support, and are followed by the base form of the main verb.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Modals are followed by the base verb	🧠 情态动词后接动词原形	She can swim.	🧠 她会游泳。
Modals do not change for third person singular	🧠 情态动词在第三人称单数时不变化	He can drive.	🧠 他会开车。
Negatives and questions use the modal itself, not do	🧠 否定和疑问直接使用情态动词本身，而不是 do	Can you help?	🧠 你能帮忙吗？
Modals express meanings beyond time, such as obligation or possibility	🧠 情态动词表达超越时间的含义，如义务或可能性	You must stop.	🧠 你必须停下。

When multiple auxiliaries appear together, English follows a common sequence. Modals come first, then perfect have, then continuous or passive be, then the main verb. Each auxiliary determines the form of the next verb, so correct order helps keep meaning clear.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Modal + have + past participle	🧠 情态动词 + have + 过去分词	She might have missed the call.	🧠 她可能错过了来电。
Modal + be + -ing	🧠 情态动词 + be + -ing	They will be waiting.	🧠 他们将一直在等待。
Modal + have + been + -ing	🧠 情态动词 + have + been + -ing	I would have been working.	🧠 我本来一直在工作。
Modal + have + been + past participle for passive perfect	🧠 情态动词 + have + been + 过去分词，构成被动完成时	The files may have been deleted.	🧠 这些文件可能已被删除。

Auxiliaries help form questions by moving to the beginning of the clause. If there is an auxiliary already, it inverts with the subject. If there is no auxiliary, do is added, and the main verb stays in the base form.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
If an auxiliary exists, invert auxiliary and subject	🧠 如果存在助动词，则将助动词与主语对调	Are you ready?	🧠 Are you ready?
With have or modals, invert the auxiliary	🧠 如有 have 或情态动词，倒置助动词	Have they arrived?	🧠 Have they arrived?
If no auxiliary exists, add do and use base verb	🧠 如果没有助动词，添加 do 并使用基本动词	Did she call you?	🧠 Did she call you?

Auxiliaries create negatives by adding not after the auxiliary. This includes be, have, do, and modals. If there is no auxiliary in a simple present or past statement, do is added and the main verb stays in the base form.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Place not after the auxiliary	🧠 将 not 放在助动词之后	She is not coming.	🧠 她不来。
Modals take not directly	🧠 情态动词直接带 not	You should not worry.	🧠 你不应该担心。
Add do if there is no auxiliary	🧠 如无助动词，添加 do	We do not know.	🧠 我们不知道。

Auxiliaries often contract in everyday English, especially with pronouns. Not also contracts with many auxiliaries. Contractions are common in speech and informal writing, while full forms are more formal or used for emphasis and clarity.

Word/Phrase	🇨🇳 中文 Word/Phrase	Definition	🇨🇳 中文 Definition	Example	🇨🇳 中文 Example
I am → I’m	🧠 I am → I’m	Be contracted with the subject	🧠 与主语结合的 Be 的缩写形式	I’m late.	🧠 I’m late.
She is → She’s	🧠 She is → She’s	Be contracted with the subject	🧠 与主语结合的 Be 的缩略形式	She’s working.	🧠 She’s working.
They have → They’ve	🧠 They have → They’ve	Have contracted with the subject	🧠 与主语结合的 Have 的缩写形式	They’ve finished.	🧠 They’ve finished.
do not → don’t	🧠 do not → don’t	Negative contraction with do	🧠 与 do 的否定缩写	I don’t agree.	🧠 I don’t agree.
will not → won’t	🧠 will not → won’t	Irregular negative contraction with will	🧠 与 will 的不规则否定缩写	He won’t come.	🧠 He won’t come.

Many auxiliary verbs can also act as main verbs. As auxiliaries, they support another verb and often help grammar like tense, questions, or negatives. As main verbs, they carry the core meaning and can appear alone, often with a different structure.

Rule	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Be can be a main verb for identity or state	🧠 Be 可以作为表示身份或状态的主要动词	She is a teacher.	🧠 She is a teacher.
Have can be a main verb for possession or experience	🧠 Have 可以作为表示占有或经历的主要动词	They have a car.	🧠 They have a car.
Do can be a main verb for actions or tasks	🧠 Do 可以作为表示行动或任务的主要动词	I do my homework.	🧠 I do my homework.
As auxiliaries, these verbs combine with another verb form	🧠 作为助动词时，这些动词与另一动词形式结合	They have eaten already.	🧠 They have eaten already.

Auxiliary verbs are be, have, do, and the modals, and they work with a main verb to build meaning and grammar. They form continuous and passive structures with be, perfect structures with have, and questions and negatives with do when needed. Modals add meanings like ability and obligation and are followed by the base verb. Recognizing auxiliaries helps you form correct questions, negatives, and multi-verb verb phrases.