A modal verb is a type of auxiliary (helping) verb that has no meaning on its own but it modifies the main verb, changes its meaning and gives more details about action.
Must is a type of auxiliary modal verb used to express certainty, necessity or strong obligation which doesn’t come from outside, it’s a personal opinion. It also expresses prohibition.
Must can be expressed in the three forms and it doesn’t change even for the third person:
The affirmative form of the verb must has this structure:
Subject + must + verb.
The negative form of the verb must has this structure:
Subject + must not + verb.
- Short form of the Negative form is: “mustn’t“
|PERSON||SHOULD + NEGATION
The interrogative form of the verb must has this structure:
Must + subject + verb + …?
- Certainty/reasonably expected
- It must be her flat. It’s number 13.
- This house must be in a good state! They renovated it last year.
- Must they be rich? They live in a luxury flat in the city center.
- Strong obligation
- I must search for a new house, my contract ends soon.
- She must clean the kids clothes, they got very dirty at the park.
- Must we be on time?
- I must buy a new fridge.
- He must search for a student flat.
- Must they paint the walls?
- Prohibition (Negative)
- You must not give your address on online forums!
- He must not surf on the net while working!
- You mustn’t smoke in this restaurant.
We use must when:
- We are sure about something, something is reasonably expected (affirmative);
- There is strong obligation (affirmative, interrogative);
- Something is necessary (affirmative, interrogative);
- Prohibition (negative).
We use the modal verb must to express certainty, necessity or strong obligation which doesn’t come from outside. Must can be expressed in the three forms (affirmative, negative and interrogative) and it doesn’t change even for the third person.
The structure for must in its three forms is:
- Affirmative: Subject + must + verb;
- Negative: Subject + must not + verb;
- Interrogative: Must + subject + verb + …?
— “I must visit my parents soon.” = The subject feels obligation about visiting her parents.
— “You must not try drugs.” = It expresses prohibition.
— “Must I do it now?” = The subject asks if he has to do it in that moment.
Let’s revise this content within the [Form] section. Take a look at the [Example] section that shows its use within a context.