Auxiliary Verbs and Modals.

BE, HAVE and DO are auxiliary verbs. Auxiliary verbs are ‘helping verbs’ and are used to give more detail about the main verb.

  1. ‘BE’ is used with the Present Continuous tense of the main verb: “I am working”.
  2. “HAVE” is used with the Perfect tenses: “I have been working”, “I had been working”.
  3. “DO” is used to form the Interrogative; both positive and negative: “Do you work?” / “No, I don’t work”.
Things to note about auxiliary verbs:
  • Auxiliary verbs can also be used as main verbs. i.e.
    • I have had a lot of English lessons.. (HAVE is the auxiliary, HAD is the main verb.)
    • How do I do this exercise? (The first DO is the auxiliary, the second DO is the main verb.)
  • Auxiliary verbs CANNOT be used WITHOUT a main verb.
  • Auxiliary verbs CANNOT be used WITH modal verbs. (See below.)
  • Auxiliary verbs are used to form the interrogative (ask questions), and the negative.
  • Auxiliary verbs are often used to change the tense of the main verb.
  • Auxiliary verbs are irregular.
    • BE = I am / you are / he, she, it is / we are / they are.
    • HAVE = I have / you have / he, she, it has / we have / they have.
    • DO = I do / you do / he, she, it does / we do / they do.



CAN, COULD / MAY, MIGHT, MUST / SHALL, SHOULD (OUGHT TO) / WILL, WOULD are the modal verbs (sometimes called ‘modal auxiliary’ verbs). They are also ‘helping verbs’, but unlike the three auxiliary verbs above, they cannot be used as main verbs.

  1. I can speak a little English. I could speak English if I studied more.
  2. I may learn to speak English. I might learn to speak it well. I must learn English.
  3. I shall learn to speak English. I should (ought to) learn it if I want a better job.
  4. I will learn to speak English. It would be easier if I did more of these lessons.


Things to note about modal verbs:
  • Modal verbs do not add an ‘s’ to the third person singular. i.e. I can / you can / he, she, it can / we can / they can.
  • Modal verbs don’t need the auxiliary DO to form the interrogative and negative. i.e. Can you speak English?
  • Modal verbs don’t have an infinitive form (except BE ABLE TO and OUGHT TO)
  • The verbs HAVE TO and NEED TO are known as ‘semi-modals’ because they don’t have all the same characteristics as the other modals.


Modal verbs in more detail:
  1. Can / Could are used for requests and to talk about the ability to do something.
    • Can I go to the party, please? (Please allow me to go.)
    • I can go to the party with you. (I am able to go.)
  2. May / Might are used for possibility / probability (improbability) and also for (polite) requests.
    • John may come to the party. (He probably will).
    • John might not come to the party. (He possibly won’t).
    • May I come to the party, please? (Please ask me to come.)
  3. Shall / Should (Ought to) / Must – are used for degrees of obligation.
    • Shall I come to the party with you? (Would you like me to?)
    • Should I come to the party with you? (Do you think it would be a good idea?)
    • Must I come to the party with you? (Is it an obligation?)
  4. Will / Would are used for predictions and conditionals.
    • John will be at the party, I am sure of it. (Prediction)
    • I would go to the party if John were going. (Conditional)


Relevant Content:

Wikipedia on Auxiliary Verbs
Wikipedia on Modal Verbs