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Modals (also known as modal verbs, modal auxiliary verbs, modal auxiliaries) are special verbs that behave irregularly in English. They usually give additional information about the function of the main verbs that follow.
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Some characteristics of modal verbs:
- They never change their form. You can't add "s", "ed", "ing"...
- They are always followed by an infinitive without "to" (i.e. the bare infinitive.)
- They are used to indicate modality and allow speakers to express certainty, possibility, willingness, obligation, necessity, ability
Examples:
I can speak German.
She can speak German. (the verb speak must not be added with ‘-s’ because of the modal verb, can)
He might come to the meeting. (the verb come must not be added with ‘-s’ because of the modal verb, might)
List of modal verbs
Can, could, may, might, will, would, shall, should, must, dare, ought to, had better, need not
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| The Use of Modal Verbs |
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To express functions like:
- Permission
- Ability
- Obligation
- Prohibition
- Lack of necessity
- Advice
- Possibility
- Probability
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| Modal Verb |
Expressing |
Examples |
| must |
Strong obligation |
You must stop when the traffic lights turn red. |
| Logical conclusion / Certainty |
He must be very tired. He's been working all day long. |
| must not |
Prohibition |
You must not smoke in the hospital. |
| can |
Ability |
I can swim. |
| Permission |
Can I use your phone, please? |
| Possibility |
Smoking can cause cancer. |
| could |
Ability in the past |
When I was younger I could run fast. |
| Polite permission |
Excuse me, could I just say something? |
| Possibility |
It could rain tomorrow! |
| may |
Permission |
May I use your phone, please? |
| Possibility, probability |
It may rain tomorrow! |
| might |
Polite permission |
Might I suggest an idea? |
| Possibility, probability |
I might go on holiday to Australia next year. |
| need not |
Lack of necessity/absence of obligation |
I need not buy tomatoes. There are plenty of tomatoes in the fridge. |
| should/ought to |
50 % obligation |
I should / ought to see a doctor. I have a terrible headache. |
| Advice |
You should / ought to revise your lessons. |
| Logical conclusion |
He should / ought to be very tired. He's been working all day long. |
| had better |
Advice |
You'd better revise your lessons |
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| Modals in the present and past |
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Modals in the Present |
Modals in the Past |
| Obligation |
You must / have to stop when the traffic lights are red. |
You had to stop. |
| Advice |
You should see a doctor. |
You should have seen a doctor |
| Prohibition |
You mustn't smoke here. |
You mustn't have smoked there. |
| Ability |
I can run fast. |
I could run fast. now I am old. |
| Certainty |
He has a Rolls Royce. He must be very rich.
He can't be American. His English is terrible. |
He must have been rich. He had a big house and an expensive car.
He can't have written that poem. He was illiterate. |
| Permission |
Can I go out? |
She could drive her father's car when she was only 15. |
| Possibility |
It may / can / could / might rain. It's cloudy. |
I guess it may / can / could / might have been Lacy on the phone. |
| Lack of Necessity |
You don't have to / needn't buy any tomatoes. There are plenty in the fridge. |
You didn't have to / didn't need to buy tomatoes. |
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Difference between must and have to
Must
1. We use must to make a logical deduction based on evidence. It indicates that the speaker is certain about something:
Examples:
- It has rained all day, it must be very cold outside.
- The weather is fantastic in Sao Paolo . It must be a lot fun to live there.
2. Must is also used to express a strong obligation.
Examples:
- Students must arrive in the examination hall on time.
- You must stop when the traffic lights are red.
- I must go to bed before 12 a.m.
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Have to
Like must, have to is used to express strong obligation, but when we use have to there is usually a sense of external obligation. Some external circumstance makes the obligation necessary.
Examples:
- I have to send an urgent email.
- I have to take this book back to the library.
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'Shall' and ' will' have the same meaning and are used to refer to the simple future. Note that 'shall' is not used often in modern English especially in American English.
The use of ‘shall’ and ‘will’
- Will is used with all persons
Example: I/you/she/he/it/we/they will go there.
- Shall is used with the first person singular and plural
Example: I/we shall go
- The short form of will and shall is ‘ll.
Examples:
I/you/she/he/it/we will/’ll call you.
I/we shall/’ll call you.
- In the negative, the short forms of will not and shall not are won’t and shan’t respectively.
Examples:
I/you/she/he/it/we/they won’t give up.
I/we shan’t give up.
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The use of shall
It should be noted that shall is often used to make suggestions, offers or ask for advice. It is used in questions as follow:
- Shall we stay or go out?
- Shall we dance?
- Shall I get his phone number if I meet him?
- What shall I do to get rid of the pests on my plants?
As said above shall is used with first person singular and plural (I and we.) But there is a very special use of shall with other persons to make a promise, command or threat as noted below:
- You shall not get in! (Command)
- You shall pay for it. (Threat)
- You shall get your money back soon. (Promise)
In American English shall is mainly used in formal or legal documents:
- You shall abide by the law.
- There shall be no trespassing on this property.
- Students shall not enter this room.
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