Introduction
Must and have to belong to the group of auxiliary modal verbs that have no meaning on their own but they modify the main verb, change its meaning and give more details about the action.
Must and have to are used to express certainty, necessity or strong obligation which comes from internal or external factors.
Form
Must and have to have different positions in the sentence in the affirmative, negative and interrogative forms.
Affirmative
In the afffirmative form their structure is:
Subject + must + verb + …
Subject + have/has to + verb + …
Negative
In the negative form their structure is:
Subject + must not + verb + …
Subject + do/does + not + have to + verb + …
Interrogative
In the interrogative form their structure is:
Must + subject + verb + …?
Do/Does + subject + have to + verb + …?
Example
Affirmative:
- I must go before she wakes up.
- I have to stop eating sweets.
Negative:
- You mustn’t read this book.
- You don’t have to do this for me.
Interrogative:
- Must you wear the same suit every day?
- Do you have to work all weekend?
Use
We use must for strong obligations and necessities that come from us, for example from our personal opinion. Mustn’t usually expresses prohibition.
We use have to for strong obligations and necessities that come from our social context, for example regulations and orders that come from someone else. Don’t have to usually expresses that it is not necessary to do something.
Summary
Must and have to are two modal verbs which are used to express strong obligation or the need to do something:
- must expresses strong obligation which comes from inside. Mustn’t usually expresses prohibition;
- have to is generally used to show that there is an obligation imposed by external factors. Don’t have to usually expresses that it is not necessary to do something.
Must and have to are followed by the base form of the verb.
For example:
— “I must start a diet, I do not like my appearance.” = The subject chooses to start a diet because of personal reasons.
— “I have to start a diet, the competition is soon.” = The subject is obliged to start a diet because of external reasons.
NOTE: The form of must is always the same, whereas have to changes to has to in the third person singular.
Let’s revise this content within the {Form} section. Take a look at the {Example} section that shows its use within a context.