Modals

Modal Verbs

CanCould Be able to May Might

ShouldOught to

PermissionPossibility, Probability Ability

Suggestion and advice

Will Shall Would

Obligation and Prohibition

Necessity

Need toHave to don't need to don't have to

MustHave to Don't have to Mustn't

Permission, Possibility and Probability

Can /can't/ cannot We use them to say that something is possible or allowed

Could We use it to say that something was possible or allowed in the past

May / Might We use these modals to say that something is possible or probable. We also use them to make polite requests.

be able to It is a synonym of can/could but a little bit more formal. Since can/could are only possible in present and past, we use be able to for all the other tenses.

Could We use could to talk about possibility in the present or future.

Ability

Can We use it to express abilities in the present. When the activity is difficult or requires a great effort we can use: manage to or succeed in + -ing

Could We use it to express general abilities in the past. For things that we were able to do once (at a particular moment in the past) we use: was/were able to

Be able to In many cases it has the same meaning as can or could. We use it to express ability in certain tenses (future, perfect tenses, etc). It is a bit more formal than can or could

Can't/Couldn't/wasn't able to We use them to describe a lack of ability

Obligation and Prohibition

Have to We use have to to talk about what is necessary or a rule. Have to describes what other people tell us to do. We express obligation or necessity in the past, future or perfect tenses using have to instead of must.

Must We use must to talk about obligation, what is necessary or important to do. Must describes what we personally think is necessary to do. Must has no past or future forms.

Mustn't Mustn't describes what is NOT allowed. It is necessary that you DON'T do it. We use it when we think something is against the rules. In speaking we often use can't instead of mustn't.

Don't have to We use it to describe what is not necessary but you can do it if you want.

Necessity

don't need to /needn't We use them to express what is NOT necessary but you can do it if you want. The two phrases have the same meaning.

Need to We use it to say what is necessary to do. Need to is not really a modal verb (we use it like any other verb) but it can be used as a modal in questions and negatives.

Suggestion and advice

Should We use should to give advice or to say what is a good idea. We also use should to say that we expect something to happen.

Ought to We use ought to as a synonym of should. Ought to is more common in British English.

Certainty

Must We use must to say that something is certain or true (normally there is evidence)

Can't We use can't when we are sure that something is NOT true (normally there is evidence)

Will/Won't

Will has several different meanings:

• PREDICTIONS - we use it to make predictions about the future (we usually don't have any evidence).
• HABITS AND ROUTINES - we use it to talk about actions that are so common or routinary that they have become predictable or annoying habits.
• WILLINGNESS AND REFUSAL - We use it to express our disposition to do or not do something.
• OFFERS - we use it to make offers.
• INFORMAL REQUESTS- We use it to make requests from people we know well.
• ORDERS AND INSTRUCTIONS - It is used to give formal instructions and orders.

Would/Wouldn't

Would has several different meanings:

• PREDICTIONS - we use would to make predictions about the future that someone made in the past.
• HABITS AND ROUTINES - we use would to talk about habits in the past.
• WILLINGNESS AND REFUSAL - We use it to express our disposition to do or not do something in the past.
• OFFERS - we use it to make offers.
• POLITE REQUESTS- We use it to make requests from people we don't know well.
• DISAGREEMENT - It is used to disagree in a polite way.
• PREFERENCES - We use it to talk about the things we like or prefer.
• HYPOTHETICAL PRESENT/FUTURE - We use it to talk about desires that are impossible or improbable in the present or future.

Shall

Shall has several different meanings:

• OFFERS - we use it to make tentative offers. It's more common in questions.
• SUGGESTIONS - we use shall in questions to make polite suggestions (specially with the pronoun "we").
• QUESTION TAGS - we use shall in question tags after "Let's".

Shall is more common in British English and in American English people prefer to use will or should.