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Auxiliary verbs: the definition and usage of auxiliary verbs

Auxiliary verbs are important elements of English grammar. However, when we mention them, we tend to think of words like "do", "does" and "did" right? Yet, English includes a wide range of auxiliary verbs beyond these commonly known ones. Join us at PREP to dive into this grammar knowledge together!

I. What are auxiliary verbs?

Auxiliary verbs in English are used to support the main verb in a sentence. The purpose of these words is to help determine the tense, person, number, negation, and form of the main verb.

Below are some auxiliary verb examples:

“Be” (am, is, are, was, were). For example: She is studying for her exams. ➡ The auxiliary verb “is” supports the main verb “studying” in the present continuous tense.
“Do” (do, does, did). For example: Did you go to the party last night? ➡ The auxiliary verb “did” is used to create questions.
“Have” (have, has, had). For example They haven’t finished their work yet. ➡ The auxiliary verb “have” negates the main verb “finished” in the present perfect tense.
Modal verbs (can, may, must, should, would,…). For example: He can hear the music from his room sometimes. ➡ The auxiliary verb “can” supports the main verb “hear” in the sentence.

II. The indicators of auxiliary verbs in English

Below are some ways to identify and distinguish auxiliary verbs in English. Please pay close attention!

Position in the sentence: Auxiliary verbs typically come before the main verb in a sentence, except when the sentence is a question. For example:
- She is studying for her exams. ➡ The auxiliary verb “is” comes before the main verb “studying”.
- Did you go to the party last night? ➡ The auxiliary verb “did” comes before the subject, then the main verb “go”.
- They haven’t finished their work yet. ➡The auxiliary verb "haven't" comes before the main verb "finished".
The presence in negative and interrogative sentences:
- Auxiliary verbs are often used in negative sentences and questions to form their negative and interrogative structures. For example:
- She is not studying for her exams. ➡ The auxiliary verb “is” is used in negative sentences.
- Do you like coffee? ➡ The auxiliary verb “do” is used in questions.
In addition, they also appear in affirmative sentences to emphasize the mentioned action. For example: I do love you.
Common forms and tenses of auxiliary verbs: Auxiliary verbs have different forms and tenses. You can recognize the four most commonly used auxiliary verbs: "be" (am, is, are, was, were), "do" (do/does, did), "have" (have, has, had) and modal verbs (can, may, might, must, should, would, have to...).

III. The functions of auxiliary verbs in English

Auxiliary verbs in English have various functions. Below are some of the main functions of auxiliary verbs:

Function	Meaning	Example
Form tenses and verb forms	Form tenses and forms of the main verbs in the sentence	She is studying for her exams. ➡ The auxiliary verb “is” forms the present continuous tense. I have visited Paris before ➡The auxiliary verb “have” forms the present perfect tense.
Form negative sentences	Form negative sentences in English.	They aren’t coming to the party. ➡ The auxiliary verb “are” is used to create negative sentences. I don’t like spicy food. ➡ The auxiliary verb “do” is used to create negative sentences.
Form interrogative sentences	Form questions in English	Do you like ice cream? ➡ The auxiliary verb “do” is used to create questions. Is she coming to the party? ➡ The auxiliary verb “is” is used to create questions.
Ensure the person and quantity	Determine the person, quantity and time of the main verb in the sentence.	He doesn’t play basketball. ➡ The auxiliary verb “does” defines the singular 3rd person and the simple present tense. They were studying all night. ➡ The auxiliary verb “were” defines the plural third person and the simple past tense.
Create the passive voice	Create the passive voice in English	The book was written by a famous author. ➡ The auxiliary verb “was” is used to create a passive structure. The house is painted by a skillful painter.

The above functions help auxiliary verbs play an important role in determining the grammar and meaning of sentences in English.

The functions of auxiliary verbs in English

IV. The usage of auxiliary verbs in English

Two types of auxiliary verbs that are most commonly used in English are modal auxiliary verbs and lexical auxiliary verbs. Let's learn about these two common types in the auxiliary verb list below together with PREP!

1. Lexical auxiliary verbs

1.1. be

“be” (am, is, are, was, were) is used in the following cases:

Auxiliary verb	Usage	Meaning
“be”	Indicate the current state or condition.	I am a student. She is tired. They are happy.
	Express the nature, characteristics, or attributes of a person or object.	He is tall. The car is red. They are intelligent.
	Identify a noun or recognize a person or object.	This is my friend. Those are my books. She was the winner.
	Describe time.	It is 3 o’clock. Today is Monday. The event was last week.
	Create the passive structure	The book is written by a famous author. The car was repaired by a mechanic.

The auxiliary verb "be" can also be used to form different tenses and verb forms, such as the present continuous (am/is/are + V-ing), simple past (was/were + V-ed), present perfect (have/has been + V-ed), and more.

1.2. do

“do” “does”, and “did” have the following functions:

Auxiliary verb	Usage	Example
“do/does/did”	Form negative sentences in the simple present and simple past tenses.	I do not like coffee. She doesn’t like eating spicy food. They did not go to the party.
	Form questions in the simple present and simple past tenses.	Do you play the guitar? Does he go swimming? Did she finish her homework?
	Determine the person and quantity of the subject of the main verb in negative and interrogative sentences. Except for the auxiliary verb "did" which is used for all persons.	She doesn’t eat meat Do they speak English? Did they have dinner?

In addition, "do/does/did" stands before the main verb in sentences to emphasize the action. For example:

I do love you.
She did do that.
He does like sweet candy.

1.3. have

Below is the usage of “have”. Let’s check it out with PREP!

Auxiliary verb

Usage

Example

“have”

Form the present perfect, past perfect, and future perfect tenses.

She has written a book.
They had finished dinner when I arrived.
By this time next year, he will have graduated from university.

Form negative or interrogative sentence structures.

Have you ever gone to Paris?
They haven’t told me about that.

2. Modal auxiliary verbs

The auxiliary verbs that express modality or can also be called modal auxiliary verbs commonly used in English are: can, could, may, might, must, ought to, had better, will, would, shall, and should. These modal auxiliary verbs are often used to express possibility, permission, obligation, or suggestion. Let's explore their usage together through some example sentences with PREP!

2.1. Can

“Can” has the negative form “cannot (can't)” and the past form “could”. Below are some examples of how the modal auxiliary verb “Can” is used:

Usage	Example
Express the ability to do something	I can swim.
Express permission, asking someone for permission to do something	Can I borrow your pen?
Express a request or suggestion	Can you help me, please?

2.2. Could

“Could” has the negative form “Could not (Couldn’t)”. “Could” functions both as the past form of “Can” as well as a modal auxiliary verb expressing possibility. Below are some examples of how the modal auxiliary verb “Could” is used:

Usage	Example
Express the ability in the past	When I was younger, I could run very fast.
Express a polite request or permission.	Could you please pass me the salt?
Express a hypothetical action or possibility in the future.	I could go to the party tomorrow if I finish my work.

2.3. May/Might

May/ Might have the negative form May not/ Might not, roughly translating to possibly or perhaps. What are some ways the modal auxiliary verbs May/ Might are used? Let's explore together!

Usage	Example
Express something that could be real or possible in the present or future.	It may/might rain later.
'May/Might + be + V-ing' is used to express something that could potentially be happening in the present or future.	He isn’t in the office. He may/might be working from home today.
Express permission requests, but 'may not' is used to deny a request or indicate prohibition.	May I borrow your phone? Students may not smoke at school.

2.4. Must

“Must” has the negative form must not (mustn't). Below are some examples of using this modal verb:

Usage	Example
Express something as necessary or obligatory to do in the present or future.	It’s late, and you must go to bed now.
Offering stressed or emphasized advice or requests.	You must finish your homework before you can go out with your friends.
Putting forward a logical, certain conclusion.	You must be careful while crossing the road. Look both ways before you cross.
Must not is used to prohibit something, something that should not be done, or to warn someone not to do something	You mustn’t use your phone while driving. It’s against the law and unsafe.

2.5. Have to

“Have to” is used to express something as necessary or obligatory. Let's take a look at how Have to is used through the chart below!

Usage	Example
Used similarly to “Must” to express notions of necessity or obligation.	I have to wake up early tomorrow for an important meeting.
Used interchangeably with Must in the future tense, present continuous tense, past tense, and present perfect tense.	We will have to study harder next semester to improve our grades.
'do' is used with 'have to' in negative and interrogative sentences.	We don’t have to attend the meeting this afternoon.

2.6. Will

Will has the negative form will not (won't), and the past form is Would. Below are some examples of using this modal verb:

Usage	Example
Express or predict future events and situations	She will travel to Paris next month to attend a conference.
Predict present habitual actions	I think he will be at the office right now
Make an immediate decision being discussed	I will buy that dress right now.
Indicate willingness or determination to do something	I will try my best to get the scholarship.
Express a promise to do something	I promise I will always be there for you when you need me.
Express threats or warnings	If you don’t finish your work on time, there will be serious consequences.

2.7 Would

Would has the negative form Would not (wouldn't). Would is both the past tense of will as well as a modal verb. Below are some examples of how Would is used:

Usage	Example
Express past hypothetical scenarios or predictions	If I won the lottery, I would buy a big house and travel around the world.
Describe past habitual actions	When I was younger, I would always ride my bike to school
Make polite requests or offers (with more formality than "will")	Would you kindly close the door behind you?
Use "Would S like/love/prefer... + to V" to politely express wants or wishes	I would prefer to have a quiet evening at home.
"Would you like to V?" as a way to make an invitation or offer	Would you like to join me for a cup of coffee?
"Would you....please?" makes a polite request.	Would you please pass me the salt?
"Would you mind + verb-ing?" makes a polite, considerate request of someone.	Would you mind turning down the volume?
"Would rather + verb" or "Would prefer + to verb" expressions for indicating preference between options.	I would rather have tomatoes than potatoes.

2.8. Shall

Shall is only used in the first person, with the negative form being Shall not (Shan’t). Below are some examples of how Shall is used:

Usage	Example
Express or predict future events/situations	Shall we meet at 6 PM tomorrow for dinner?
Ask for advice, opinions, or suggestions	What shall we do to solve this problem?
Use "Shall I...?" when making a suggestion	Shall I book a table for us at the restaurant?
Use "Shall we...?" when proposing an idea or plan	Shall we take a break and grab a cup of coffee?

2.9. Should

Should has the negative form Should not (shouldn’t), loosely translated as expressing what is best or recommended to do. Below are some examples of using Should:

Usage	Example
Express obligation or necessity, though less strong than Must or Have to.	You should eat more fruits and vegetables for a healthier diet.
Ask for advice, opinions, or suggestions in a question form.	Should I call the doctor for an appointment?

V. Special cases

Below are some words that function as both regular verbs and modal auxiliary verbs depending on context:

Special case	Usage	Example
Need	Need V: Considered a modal verb denoting necessity.	You needn’t clean that car
Dare	Dare V: Also considered a modal verb, though the construction "Dare + bare infinitive" is less common.	Dare you tell him?
Used to	Used to V: Describes habitual past actions.	I used to play the piano when I was younger.
Used to	Used S to V?: Also functions as a modal verb in questions.	Did you use to go there?
Ought to	Ought to V: Suggests or recommends an action, similar to "should.”	You ought to apologize for what you said.
	(-): Ought not to V (Oughtn’t) to V	You ought not to smoke in public places.
	(?): Ought S to V?	Ought I to call her and check on her?

VI. Exercises on auxiliary verbs with detailed answers

Exercise 1: Complete the following sentences with the appropriate form of “can” or “could”.

She _____ speak five languages fluently.
_____ you please open the window?
When I was younger, I _____ run for hours without getting tired.
_____ you lend me your pen, please?
I’m not sure if I _____ attend the meeting tomorrow.

Exercise 2: Fill “can”, “could” or “might” in the appropriate blanks

It _____ rain later, so we should bring umbrellas.
_____ you please pass me the salt?
I’m not sure if I _____ make it to the party tonight.
When I was younger, I _____ climb trees.
_____ I use your phone to make a call?

Exercise 3: Complete the following sentences with the appropriate form of “do, does, did”.

She _____ her homework every day.
_____ they play soccer on weekends?
He _____ his breakfast this morning.
_____ you like to dance?
We _____ a great time at the party last night.

Answer keys:

Exercise 1	Exercise 2	Exercise 3
can Could could Could can	might Could could could Can	does Do did Do had

Hopefully, the article about auxiliary verbs provided by PREP above has helped you understand more deeply the meaning and usage of this grammatical item. Keep looking forward to PREP's upcoming articles!

Master Tu Pham

Founder/CEO at Prep

Founder of Prep Smart Test Preparation Platform. With over 10 years of experience in teaching and test preparation, Mr. Tú has helped thousands of students achieve high scores in the IELTS exam. In addition, Mr. Tú Phạm is also a consulting expert in British Council programs and a speaker at many leading educational events, programs, and conferences.