1 of 10

Modal Verbs:

Obligation, necessity and permission.

2 of 10

Must and musn´t

Strong Obligation

3 of 10

Must and musn´t

Must

*Affirmative form:

Subject +must + verb (inf) + complement

Examples:

- You must go

- You must visit us soon

Mustn´t

*Negative form:

subject + mustn´t + verb (inf) + complement

Examples:

- You mustn´t go to that meeting.

-We musn´t be late

Interrogative form

Must + subject + verb (inf) + complement?

Examples:

- Must you live now?

- Must you travel to Barcelona tomorrow?

4 of 10

Must and mustn´t

Must is used to talk about strong obligations in the present and future that are imposed by the speaker.

The negative form of "must" expresses the idea that something is prohibitied.

5 of 10

Should, Shouldn't

and Ought to

Weak Obligation.

6 of 10

Should and Shouldn't

Should

*Affirmative form:

Subject + should + verb (inf) + complement

Examples:

- (You look tired) You should take a nap.

- I should study for tomorrow's test.

Shouldn't

*Negative form:

subject + shouldn't + verb (inf) + complement

Examples:

- You shouldn't run in the hallways

- You shouldn't have talk to him like that.

Interrogative form

Should + subject + verb (inf) + complement?

Examples:

- Should I talk to him? - Should I tell Mary about it?

-Yes, you should - Yes, you should

-No, you shouldn't - No you shouldn't

7 of 10

Should and Shouldn't

Give suggestion on what is the right thing for somebody to do.

Give advise or talk about what we think is right or wrong.

Make orders and instructions more polite

8 of 10

Ought to

*Affirmative form:

Subject + ought to + verb (inf) + complement

Example:

-You ought to drive carefully

-You ought to clean your room before you leave.

*Hardly ever used in negative form:

Subject + ought not/oughtn't to + verb (inf) + complement

Example:

-We ought not/oughtn't to have agreed without knowing what it would cost.

*NOT USED in interrogative form.

9 of 10

Differences

Ought to

You suggest someone what is one of the last options one has or something that one can't easily avoid, for example, any longer.

It is more explicit, similiar to a request.

Example:

-You ought to tell her how you feel.

(You can't avoid telling her how you feel)

Should

You suggest someone that something is good to be done or something that after all is meaningful.

It is not as explicit as ought to.

Example:

- You should tell her how you feel.

(It is better or the best to tell her how you feel)

10 of 10

Let's practice!

Create 3 sentences using "should" and "shouldn't"

-

Create 3 sentences using "ought to"

-

Create 3 sentences using "must and mustn´t

-