Auxiliary verbs
An auxiliary verb, or "helping verb", is a verb used together with a main verb to form tenses, questions, negatives and passives. English has three primary auxiliaries (be, have, do) and modal auxiliaries (can, will, must, should, and others). They add grammatical meaning such as time, possibility or emphasis rather than describing the main action itself.
Types of auxiliary verbs
Primary auxiliary: be
Used to form continuous tenses and the passive voice.
e.g. She is studying, The letter was sent
Primary auxiliary: have
Used to form perfect tenses.
e.g. They have finished, He had already left
Primary auxiliary: do
Used to form questions, negatives and emphasis in simple tenses.
e.g. Do you agree?, I did not know, I do like it
Modal auxiliaries
Add meaning such as ability, permission, possibility, obligation or advice; they never change form and are followed by a base verb.
e.g. can swim, must leave, should apologise
Semi-modal auxiliaries
Modal-like expressions built with be or have that behave partly like modals in meaning.
e.g. have to go, be able to attend, used to smoke
Rules to remember
- Auxiliary verbs are always followed by another verb form: be + -ing, have + past participle, do + base form, or a modal + base form.
- In questions, the auxiliary moves before the subject: 'Have you seen it?' not 'You have seen it?'.
- In negatives, 'not' is placed directly after the auxiliary: 'She has not called' or 'They cannot come'.
- Modal auxiliaries do not add -s, -ed or -ing, and are never followed by 'to' (except semi-modals like 'have to' or 'be able to').
- When there is no other auxiliary present, 'do' is inserted to form questions and negatives in the present simple and past simple: 'Does he work here?', 'I don't know'.
Examples in sentences
| Example | How it works |
|---|---|
| I am writing a report for my manager. | 'am' is the auxiliary forming the present continuous with 'writing'. |
| We have visited that museum twice. | 'have' is the auxiliary forming the present perfect with 'visited'. |
| Do you understand the instructions? | 'do' is the auxiliary used to form a question in the present simple. |
| The report was completed on time. | 'was' is the auxiliary forming the passive voice with 'completed'. |
| You should check your answers before submitting. | 'should' is a modal auxiliary expressing advice. |
| She did not attend the meeting yesterday. | 'did' is the auxiliary forming the negative in the past simple. |
| They must have left already. | modal auxiliary 'must' combines with 'have' to express confident deduction about the past. |
Common mistakes
Incorrect: She can to speak French.
Correct: She can speak French.
Incorrect: You have seen him?
Correct: Have you seen him?
Incorrect: He don't like coffee.
Correct: He doesn't like coffee.
Why this matters for IELTS
Using auxiliary verbs accurately across a range of tenses, passives and modal forms is a key part of the Grammatical Range and Accuracy criterion in IELTS Writing and Speaking. Examiners look for correct question formation, consistent subject-auxiliary agreement, and natural modal use to express certainty, obligation or possibility. Errors like omitting 'do' in negatives or misplacing auxiliaries in questions signal lower accuracy, so practising clean auxiliary use helps you demonstrate the wider range needed for Band 7 and above.
Frequently asked questions
What is an auxiliary verb in simple terms?
It is a helping verb, such as be, have, do or a modal, that works with a main verb to show tense, form questions, make negatives or build the passive voice.
What is the difference between auxiliary verbs and modal verbs?
Modal verbs (can, must, should, and others) are a specific type of auxiliary verb that express meanings like ability, permission or obligation, while be, have and do are called primary auxiliaries and mainly build tenses, questions and negatives.
Can a verb be both a main verb and an auxiliary verb?
Yes. Be, have and do can act as main verbs with their own meaning, for example 'I have a car', or as auxiliaries helping another verb, for example 'I have finished my work'.
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