Modal Auxiliaries

Modal auxiliary verbs are a type of helping verbs which are used to express manners, ability, politeness, possibility, permission or obligation. 

They express modality. Modality is the way in which something happens. Modality in the speaker’s voice gives us an idea of the person’s mood. 

The main auxiliary verbs are:

• Can/ could 
• May/ might 
• Shall/ should 
• Will/ would 
• Must and have to 
• Ought to 

Characteristics of Modal Verbs 

Modals never change their form. This means that we cannot add –s, -es or –ed after modals. 

For example:

• She will come to school is correct. 
• She wills come to school is wrong. 

A modal verb is always followed by the base form of a verb. 

For example:

• I can read the book in a day. 

Uses of Modal Verbs 

“Can” or “can’t” are used to express the ability or lack of ability to do something. These are used in present and future tense. 

For example:

• Shawn can sing. 
• Amanda can’t speak Spanish. 

We use “could” or “couldn’t”, in the past tense, to express the ability or inability to do something. 

For example:

• When I was young, I could do all the work myself. 
• I couldn’t visit my brother when I went to Texas. 

“Can” or “could” are used for: 

Taking and giving permissions. 

For example:

• Can I borrow your pen? 
• You can use my pen. 

Making suggestions.

For example:

• You could visit the Niagara falls tomorrow. 

Modals used to express formal permission or formal prohibition.

May and Might 

You may leave the office at 5pm. (The speaker is giving formal permission to the listener.) 

You may not use phone during working hours. (The speaker is formally prohibiting the listener from using phone at work.) 

May or might are used to make polite requests. 

For example:

• May I help you? 

Shall/ should/ ought to 

Shall is used for a polite suggestion when we are quite sure of a positive answer. 

For example:

• Shall I go to play? 

Should is used:  

For a polite suggestion when we are not so sure of a positive answer. 

For example:

• Should I buy something? 

To give advice. 

For example:

• You should respect your elders. 

Shouldn’t is used to give advice about something that is wrong or unacceptable. 

For example:

• You shouldn’t waste food. 

Will/ would 

Will is used to make a statement about which we are certain or determined. 

For example:

• I will finish the work by evening. 

Would or wouldn’t is used to denote a past action which was habitual. 

For example:

• When I was a kid, I would play guitar. 
• She wouldn’t sit idle when she was a kid. 

“Used to” can replace “would”. 

For example:

• I used to play guitar when I was a kid. 

Must/ have to/ need to 

These are used to express need or requirement. 

For example:

• You must wash your hands before and after food. 
• You have to reach the office at 10 am. 
• You need to give your address so that I can send the mail. 

Must is used to express statements about which the speaker is very sure. 

For example:

• William has sung many songs. His voice must be excellent. 

Must not is used to talk about something that is forbidden. 

For example:

• You must not use phone while driving. 

The past form of must is “had to” and “needed to”. 

For example:

• I had to wait for a long time at the bus stop. 
• I needed to try hard to finish the work on time.