What are Modal Auxiliary Verbs? Rules and Examples

Verbs in English are divided into two categories main verb and auxiliary verb. Auxiliary verbs are further divided into two types primary and modal auxiliary verbs. This article will explain the form and uses of modal auxiliary verbs. Moreover, you’ll learn how modal auxiliaries (can, may, should, might, etc.) can be differentiated from other auxiliary verbs (is, am and are, have, has and had, and do), as well as from main verbs.
What are Modal Auxiliary Verbs? Rules and Examples
What are Modal Auxiliary Verbs?
The modal verbs are helping or auxiliary verbs that add a wide range of meanings to the main verb, such as permission, ability, possibility, necessity, request, offers, obligation, etc. Modal auxiliary verbs are used before main verbs and change their meaning in a sentence. Most of the modal verbs have several meanings. 
Take some examples of how a modal verb alters the meaning of the main verb. 
Compare the following two sentences.
  • She cooked something delicious. (simple past tense)
  • She may cook something delicious. (present subjunctive tense)
The difference between cooked and may cook is that with cooked, we indicate that indeed something delicious was cooked. In the second sentence with may cook, we indicate that the ‘cooking something delicious‘ has not occurred yet but may cook express whether the situation is possible or hypothetical. In other words, we are not sure something delicious will be cooked.
  • I can study all night during the semester.
  • I study all night during the semester.
The first sentence contains the modal verb ‘can‘ that indicates I have the ability or potential to study all night during the semester. The second sentence does not contain a modal verb that indicates it is a straightforward statement.

Modal Verbs Meaning

We use modal verbs to talk about probability, possibility, etc., of situations and events. We do not generally use modal verbs to report situations and events or to say that situations definitely exist or that particular events have definitely happened. Modal verbs have mainly two kinds of meaning certainty and obligation and freedom. We use model verbs to say that a situation is possible, impossible, probable, or certain.  For example
  • She must be tired.
  • I might go to London next summer.
  • It can’t be true.
The second meaning of modal verbs is obligation and freedom, which means telling or advising people to do or not to do something, and talking about freedom or ability to do something. With these meanings, modal verbs are essential in the expression that gives instructions or suggestions and makes requests or invitations.
  • You should rest for a few days.
  • Can I sit here?
  • Would you like to attend the party?

List of Modal Verbs

The following is the list of modal auxiliary verbs. Some of them are semi-modals verbs.
  • will
  • would
  • can
  • could
  • may
  • might
  • shall
  • should
  • must
  • dare
  • ought to
  • used to
  • need or need to
  • have/had to
Each model verb has a somewhat different meaning and uses. Even though these model verbs can be seen as sets (will/would, can/could, shall/should, may/might), each of these, no matter in which form it, can express a ‘present’ or ‘future’ meaning.
All Modal Verbs Suggest
  • Ability
  • Obligation
  • Permission
  • Suggestion
  • Advice
  • Promise
  • Intention
  • Request
  • Possibility
  • Necessity,
  • Compulsion
  • Prohibition
  • Wish
  • Duty
Note: In indirect speech, we use could, should, might, and would as past forms of can, shall, may, and will, but they aren’t generally used as past forms. We use could, should, might, and would for less definite meaning.

Rules of Using Modal Auxiliary Verbs (Modal Verbs Rules)

Remember the following 7 rules of modal verbs while using them.

Rule-1: We do not add -s to a modal verb in the third person singular.
  • He may be here next week. (not he mays)
  • It might snow this evening. (neither modal nor the main verb takes -s)
Rule-2: We made questions, short answers, negative, and tags without do.
  • May I stay with him? (Not Do I may)
  • Can you see the moon?
  • Could I work in the circus?
Rules-3: Modal verbs are always followed by the main verb in its base form. Modal verb cannot be used with the main verb that is in a past tense
  • We should visit the museum.
  • When I went into the kitchen, I could smell burning.
To provide some of the modal meanings in the past, we have to use other verbs because modal verbs do not have past tense forms. For example, if we want to express past necessity, we need to use had to, not must.
  • You must meet the professor today.
  • You had to meet the professor yesterday. (had to past necessity)
Rules-4: Negative sentences are formed by adding “not” between modal and main verb.
  • I could not find my books this morning.
  • The paper may not be difficult.
  • Don’t drink – it might not be clean.
Rules-5: To form questions by swapping the subject and modal verb.
  • Might I ask a question?
  • Should I apologize to her? Yes, I think you should.
After modal verbs in a sentence, always use the infinitive (without to) of other verbs except the modal verb ought.
  • You must water the flower daily.
  • We thought he might like to join us for lunch.
Rule-6: Ordering of Model Auxiliary Verbs
a) A modal auxiliary verb comes before any other auxiliary verb in a sentence.
b) Perfect have comes after a modal auxiliary.
Example: Why didn’t you apply for the job? You could have got it.
Progressive’ be’ comes after a modal verb.
Example: He could be writing a letter to his brother.
Remember these patterns with modal verbs.
Statement: Affirmative/Positive (Subject + Modal + Main Verb + (rest of the sentence)You should see a doctor.
Statement: Negative (Subject + Modal + not + Main Verb + (rest of the sentence)You shouldn’t choose a weak password.
Yes/No Question (Modal + Subject + Main Verb + (rest of the sentence)Should you have the report ready by tomorrow? “Yes, you should.”
W-H Questions(W-H word + Modal + Subject + Main Verb + (rest of the sentence)Why should I choose this course?
Negative W-H Questions (W-H word + Modal + Not + Subject + Main Verb + (rest of the sentence)Why shouldn’t I choose my name?
Subject Questions (Who + Modal + Main Verb + (rest of the sentence)Who should stay here tonight?
Rule-7: Modal verbs have no infinitives or participles. Instead, we use some other expression such as have to, be allowed to, or be able to.
  • Will you be able to cope with the work?
  • My brother has always been allowed to purchase what he wanted.
Using the perfect infinitive, we can make a special past form of modal verbs.
  • He should have told us.
  • He must have missed his paper.
  • I shouldn’t have any difficulty with this assignment.

Examples of Using Modal Verbs

There are many reasons to use modal verbs in our writing. The modal verbs can give a degree of probability, express possibility and impossibility, give advice, make predications and interferences, grant permission and make requests, etc. The following are examples of modal verbs that add special elements of meaning to the main verb.

Using Modal Verbs to Express Ability and Obligation

  • I can play the guitar. (present ability)
  • I can speak German. (the modal ‘can’ describe knowledge)
  • I couldn’t speak French well two years ago, but now I can. (past ability)
  • I can’t meet him today, but I can see him next week. (can use for future ability)
  • You must not use too much water. (obligation)
  • I have to apply for a passport this month.

Using Modal Verbs to Express Possibility and Certainty

The modal verbs can, could, may (have), might (have), and must (have) are used to express possibility and certainty in the past, present, and future, respectively.
You can see the university building from the top of that hill.
  • The documents could arrive next Friday.
  • She may not know the correct answer.
  • It must be 6. (I am certain the answer is 6)
  • That boy might be your brother. (It’s possible that he is your brother)
  • This book could improve your general knowledge. (future possibility)
  • The girl might have been Sara. (It’s possible that the girl was Sara)

Using Modal Verbs to Ask or Give Advice and Permission and Make Request

  • Can I take your umbrella, David? Yes, you can.
  • Could I possibly borrow your bike? (Asking permission using could is more polite than can)
  • May I have some sandwiches?
  • What should we do now? (ask for advice)
  • You ought to be polite. (give advice)
  • He shouldn’t eat the rice if he doesn’t like it.
  • They shouldn’t have opened it. (They did open it, unfortunately)

Using Modal Verbs to Talk About Rules and Law

  • You must never cross that barrier.
  • I can’t go with him.

Using Modal Verbs to Make a Prohibition

  • You shouldn’t enter the building without permission.
  • She must not wait here.

Using Modal Verbs in Tags and Short Answers

  • ‘She can ride, can’t she? ‘Yes, she can.’
  • ‘He shouldn’t be late, should he?’ ‘No, he shouldn’t.’

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