Modals of obligation
Must and Have to
Must
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 in the negative form.
Affirmative
The structure is:
Subject + must + verb + …
- I/You must work
- He/She/It must work
- We/You/They must work
For example:
“I must visit my parents soon.” = The subject feels obligation.
Negative
The structure is:
Subject + must not + verb + …
- I/You must not work
- He/She/It must not work
- We/You/They must not work
Short form of the negative form is: mustn’t.
For example:
“You must not try drugs.” = It expresses prohibition.
Interrogative
The structure is:
Must + subject + verb + …?
- Must I/you work …?
- Must he/she/it work …?
- Must we/you/they work …?
For example:
“Must I do it now?” = The subject asks if he has to do it in that moment.
Have to
Have to is a type of auxiliary modal verb used to express certainty, necessity or strong obligation which comes from outside, from external factors.
Affirmative
The structure is:
Subject + have/has to + verb + …
- I/You have to work
- He/She/It has to work
- We/You/They have to work
Negative
The structure is:
Subject + do/does + not + have to + verb + …
Subject do/does + not have to Verb I/You do not have to work He/She/It does not have to work We/You/They do not have to work
Interrogative
The structure is:
Do/Does + subject + have to + verb + …?
- Do I/you have to work …?
- Does he/she/it have to work …?
- Do we/you/they have to work …?
