Introduction
Modal auxiliaries (can, could, may, might, shall, should, will, would, must, ought to, need, dare) show ability, permission, possibility, obligation and advice. They are the backbone of many NTRCA sentence-completion items. This lesson also covers question tags, which appear regularly in error-correction and fill-in questions.
Meanings of the main modals
| Modal | Main meanings | Example |
|---|---|---|
| can | ability, general possibility, informal permission | She can play the violin. |
| could | past ability, polite request | Could you help me? |
| may | permission, possibility, wish | May I come in? May you succeed! |
| might | weak possibility, past of may | He might come later. |
| shall | offers with I or we, a firm promise | Shall I open the window? |
| should | advice, duty, expectation | You should respect your teachers. |
| will | future, willingness, request | Will you lend me a pen? |
| would | past habit, polite request, conditional | He would visit us every Friday. |
| must | strong obligation, strong deduction | You must obey the law. He must be tired. |
| ought to | moral duty | We ought to help the poor. |
| need | necessity (mainly in negatives and questions) | You need not come. Need I go? |
| dare | have the courage (mainly in negatives and questions) | He dare not speak. |
| used to | a past habit that is no longer true | He used to smoke. |
Modal + have + V3: talking about the past
| Structure | Meaning | Example |
|---|---|---|
| must have + V3 | certain deduction | He must have missed the train. |
| may/might have + V3 | possibility | She may have forgotten the date. |
| can't/couldn't have + V3 | impossible deduction | He can't have done it. He was abroad. |
| should have + V3 | a duty not done | You should have listened to me. |
| shouldn't have + V3 | a mistake made | I shouldn't have said that. |
| needn't have + V3 | an action that was unnecessary | You needn't have brought a gift. |
| would have + V3 | an unreal past result | I would have helped you if I had known. |
| could have + V3 | a missed possibility | You could have won. |
Question tags
- A positive statement takes a negative tag, and a negative statement takes a positive tag: He is honest, isn't he? He is not honest, is he?
- Use the same auxiliary as the statement. If there is none, use do, does or did: She plays well, doesn't she? They went home, didn't they?
- I am becomes aren't I: I am late, aren't I?
- Let's becomes shall we: Let's go, shall we?
- A command takes will you: Close the door, will you? A negative command takes will you as well.
- Nobody, no one, everybody, somebody take they: Everybody came, didn't they?
- There is repeated: There is a problem, isn't there?
- Must becomes needn't or mustn't, depending on the meaning.
- Words such as hardly, seldom, never, rarely, little make the statement negative, so the tag is positive: He never lies, does he?
Common exam traps
- He must to go. Wrong. A modal is followed by the bare infinitive.
- He can swims. Wrong. A modal never takes -s.
- You should have went. Wrong. After should have, use V3: should have gone.
- She used to going. Wrong. Used to takes V1: used to go.
- Nobody came, didn't they? Wrong. Nobody is negative, so the tag is positive: did they?
Memory tips
- Modal, then V1. No -s, no to, no -ing after a modal.
- Have + V3 looks back. Modal + have + V3 is about the past.
- Flip the polarity in tags. Positive statement, negative tag. Negative statement, positive tag.
- Special tags: I am, aren't I; Let's, shall we; command, will you.
Solved examples
Example 1. You ____ not smoke here. Answer: must. The sentence expresses prohibition.
Example 2. He is not at home. He ____ have gone out. Answer: may or might. It is a possibility, not a certainty.
Example 3. Add a tag: He hardly ever writes to us, ____? Answer: does he. Hardly ever is negative, so the tag is positive.
Example 4. Add a tag: Open the window, ____? Answer: will you.
Practice problems
- Add a tag: You have finished your work, ____?
- Add a tag: There are no mistakes, ____?
- Add a tag: She never comes late, ____?
- I ____ have called you, but I forgot the number. (could / must / need)
- Correct: He can to speak French.
Answers: 1. haven't you. 2. are there. 3. does she. 4. could. 5. He can speak French.
Practice MCQs with solutions
Note: these are practice questions written in the style of past NTRCA/BCS preliminary papers. Please cross-check with the official question bank.
Question 1. You ____ have told me earlier; now it is too late.
- (a) should
- (b) must
- (c) can
- (d) may
Correct answer: (a) should
Explanation: Should have + V3 expresses a missed duty or criticism about the past.
Question 2. The light is on, so he ____ be at home.
- (a) must
- (b) should
- (c) would
- (d) need
Correct answer: (a) must
Explanation: Must shows strong logical deduction.
Question 3. She is a good swimmer; she ____ swim across the river.
- (a) can
- (b) may
- (c) must
- (d) shall
Correct answer: (a) can
Explanation: Can expresses ability.
Question 4. ____ I use your pen?
- (a) Shall
- (b) Will
- (c) May
- (d) Would
Correct answer: (c) May
Explanation: May I is the polite way to ask for permission.
Question 5. You ____ not park here; it is prohibited.
- (a) need
- (b) must
- (c) dare
- (d) might
Correct answer: (b) must
Explanation: Must not expresses prohibition.
Question 6. She can swim, ____?
- (a) can she
- (b) can't she
- (c) isn't she
- (d) doesn't she
Correct answer: (b) can't she
Explanation: A positive statement takes a negative tag with the same auxiliary.
Question 7. Let's go out, ____?
- (a) will we
- (b) shall we
- (c) don't we
- (d) let we
Correct answer: (b) shall we
Explanation: The tag for Let's is shall we.
Question 8. Nobody called, ____?
- (a) didn't they
- (b) did he
- (c) did they
- (d) was it
Correct answer: (c) did they
Explanation: Nobody is negative, so the tag is positive, and nobody takes they.
Question 9. He ____ to smoke, but he has given it up.
- (a) used
- (b) was used
- (c) is used
- (d) uses
Correct answer: (a) used
Explanation: Used to + V1 is a past habit that no longer exists.
Key takeaways
- A modal is followed by the bare infinitive, with no to, no -s and no -ing.
- Use modal + have + V3 to talk about the past.
- In tags, flip the polarity and repeat the auxiliary.
- Learn the special tags: aren't I, shall we, will you, and they for nobody and everybody.