Modal Auxiliaries

Modal verbs are a kind of auxiliary verb. They facilitate the main verb for suggesting potential, expectation, permission, ability, possibility, and obligation.

When used with the main verb, modal verbs do not end with -s for the third-person singular.  Modal auxiliary verbs never change form, but they have a different form for past tense.

The modal auxiliaries include:

NB: The words in parentheses ( ) are semi-modals. They have the same meaning, but they are different grammatically.

Will – Would

Will indicates a ‘willingness’ to do something in the future. The negative form of will – will not (won’t) indicates an ‘unwillingness’ (refusal, reluctance) to do something.

Example:

• I will give you another opportunity.
• I will play tomorrow.
• They will arrive at 10 AM.
• She won’t come today.

Would indicates general or repeated willingness in the past. It also indicates preference in the present.  

Example:

• If you did not leave, I would still be taking care of you.
• Whenever I had to go there, they would throw a party.
• We thought that people would buy this book.
• If I were you, I would not do it.
• I would like to make a toast.

Used to sometimes replaces would but sometimes it would be grammatically incorrect if we use used to in place of would.  

Example:

• When I was in school, I used to make sketches.
• He often used to cry at night without reason.
• I used to take a break at this time of the year.

Can – Could – May – Might

These modals express possibility and ability.

Can indicates ability. Could indicates ability with an option.

Example:

• I can do it. (The subject ‘I’ is sure about his/her ability)
• I could do it. (The subject ‘I’ is not sure about his/her ability)
• They cannot do it. (present)
• They could not do it. (past)

Can & could also indicate possibility.

Example:

• The temperature can rise this month.
• They can’t go too far by now.
• It could rain later.

May and might both indicate possibility but might can suggest that there is less possibility than may.  

Example:

• It may rain later.
• It might rain later.
• They may come back.
• They might come back.

Must

Must indicates necessity.

Example:

• I must leave now.
• He must study hard.
• Alex must go home by 6.00 pm.

Have to has the similar meaning to must but implies less urgency.  

Example:

• I have to leave now.
• He has to study hard.
• Alex has to go by 6.00 pm.
• I had to leave then. (past)
• He had to study hard to pass the exam. (past)

Should

Should indicates obligation and probability.

Example:

• You should come home early.
• You should not smoke at all.
• I should visit my parents more often.
• There should be an extra key for the lock in the drawer. (probability)
• He should have reached by now. (probability)
• I should have done that. (obligation in the past)

Ought to and had better sometimes replaces should.

Example:

• You ought to come home early.
• We ought to have taken a taxi. (Past)
• We had better leave. (Had better is generally used in spoken English.)
• I think parents ought to give children more freedom. (Had better won’t be appropriate here.