Defective verbs

1. Definition of Modal Verbs

Modal verbs are a special type of verb that accompany and support the main verb in a sentence, rather than functioning independently as the main verb.

Common modal verbs in English include:

Can	Could	May	Might	Must
Ought to	Should	Shall	Would	Will

Modal verbs differ from regular verbs in several ways. Let's explore their characteristics below.

2. General Structure of Modal Verbs

2.1. General Structure

S + Modal Verb + V(bare-infinitive)

• (bare-infinitive: verb without “to”)

Example:

• They can speak French and English.

2.2. No Change in Form Across Persons

Example:

• He can use our phone. (Not: He cans use your phone)

2.3. Exist in Present and Simple Past Tenses

Example:

• She can cook meals.
• She could cook meals when she was twelve.

3. Common Modal Verbs

3.1. Can

• CAN has only two tenses: Present and Simple Past. For other forms, the equivalent verb “be able to” is used. CAN can also function as an auxiliary verb for specific expressions.

Usage	Example
CAN and COULD mean “be able to,” expressing ability.	Can you swim? She could ride a bicycle when she was five years old.
In colloquial speech, CAN can replace MAY to express permission, and CANNOT to express prohibition.	In London buses, you can smoke on the upper deck, but you can’t smoke downstairs.
CAN also expresses possibility. In questions and exclamations, CAN means “Is it possible…?”	Can it be true?
CANNOT expresses virtual impossibility.	He can’t have missed the way. I explained the route carefully.
When used with verbs of perception, CAN conveys a meaning equivalent to the Continuous Tense.	Listen! I think I can hear the sound of the sea. (Not: I am hearing)

3.2. Could

Usage	Example
COULD is the simple past of CAN.	She could swim when she was five.
COULD is used in conditional sentences.	If you tried, you could do that work.
In informal speech, COULD is considered more polite than CAN.	Can you change a 20-dollar note for me, please? Could you tell me the right time, please?
COULD expresses doubt or mild objection.	His story could be true, but I hardly think it is.
COULD – WAS/WERE ABLE TO: + If describing ability or knowledge, COULD is more common than WAS/WERE ABLE TO. + If implying success in performing an action, WAS/WERE ABLE TO is used, not COULD.	The door was locked, and I couldn’t open it. I finished my work early and so was able to go to the pub with my friends.

3.3. May - Might

Usage	Example
MAY and its past form MIGHT express permission.	May I take this book? – Yes, you may. She asked if she might go to the party.
MAY/MIGHT express possibility or impossibility.	May I take this book? – Yes, you may. She asked if she might go to the party.
In exclamations, MAY/MIGHT express a wish.	May all your dreams come true!
MAY/MIGHT are used in clauses following verbs like hope and trust.	I trust (hope) that you may find this information useful. He trusted (hoped) that we might find the plan to our satisfaction.
MAY/MIGHT can replace adverb clauses of concession.	He may be poor, but he is honest. (Though he is poor…) Try as he might, he could not pass the examination. (Though he tried hard…)
MAY/MIGHT are often used in adverb clauses of purpose. In such cases, CAN/COULD can replace MAY/MIGHT.	She was studying so that she might read English books.
MIGHT (not MAY) is sometimes used to express petulant reproach.	You might listen when I am talking to you. You might try to be a little more helpful.

3.4. Must

Usage	Example
MUST means “must,” expressing a command or obligation.	You must drive on the left in London.
MUST is used in logical conclusions.	Are you going home at midnight? You must be mad!
MUST NOT (MUSTN’T) expresses prohibition.	You mustn’t walk on the grass.
To express the negative of MUST meaning “not necessary,” use NEED NOT (NEEDN’T).	Must I do it now? – No, you needn’t. Tomorrow will be soon enough.

3.5. Shall

Usage	Example
Used in the Simple Future tense for the first person.	I shall do what I like.
Expresses a promise, determination, or threat.	If you work hard, you shall have a holiday on Saturday. (promise) He shall suffer for this; he shall pay you what he owes you. (threat) These people want to buy my house, but they shan’t have it. (determination)

3.6. Should

Usage	Example
Used to advise someone to do something, equivalent to ought to.	You should do what the teacher tells you.
Used instead of must when a less forceful obligation is intended.	Members who want tickets for the dance should apply before September 1st to the Secretary.

3.7. Will

Usage	Example
Used in the Simple Future tense to express a plan, willingness, promise, or determination.	All right; I will pay you at the rate you ask. (willingness) I won’t forget little Margaret’s birthday. I will send her a present. (promise)
Used in requests.	Will you shut the door?

3.8. Would

Usage	Example
Used to form the Future in the Past or in conditional sentences.	He said he would send it to me, but he didn’t. If she were here, she would help us. He would have been very happy if he had known about it.
Expresses a past habit, interchangeable with used to.	Every day he would get up at six o’clock and light the fire.

3.9. Ought to

Usage	Example
OUGHT TO expresses strong probability.	If Alice left home at 9:00, she ought to be here any minute now.
OUGHT TO can be used for the future with time expressions like tomorrow, next Tuesday.	Our team ought to win the match tomorrow.
OUGHT NOT TO HAVE + past participle expresses disapproval of a past action.	You ought not to have spent all that money on such a thing.

OUGHT TO means “should,” similar to should. In most cases, OUGHT TO can be replaced by should.

Example:

• They ought to (should) pay the money.
• He ought to (should) be ashamed of himself.