must, have to, mustn't, needn't
1. The use of must, must not (mustn't) and need not (needn't)
The modals must, must not and need not have the same form regardless the subject. There is no ending with he/she/it.
► If you want to say the sth. is unnecessary, use need not, not must not. (The negation of must means not allowed to.)
I must play football. = I have to play football. *
I need not play football. = I do not need to play football. = I do not have to play football.
I must not play football. = I am not allowed to play football.
You can use must only with Simple Present. If you want to use it with other tenses, you need the form have to. This form is not the same regardless the subject. Look at the following table.
Modal | Substitutes |
---|---|
I must play football. * | I have to play football. * |
I need not play football. | I do not need to play football. |
I do not have to play football. | |
I must not play football. | I am not allowed to play football. |
The modal must can be used in the Simple Present only, so use the substitute have to with other tenses. The form have to has the same form regardless the subject.
Pronouns | Modal | Substitutes in the Simple Present |
---|---|---|
I, we, you, they | I must play football. * | I have to play football. * |
he, she, it | He must play football. * | He has to play football. * |
* see also point 3 below
2. Sentences and questions with have to
2.1. have to in the Simple Present
Pronouns | Affirmative sentences | Negative sentences | Questions |
---|---|---|---|
I, we, you, they | I have to get up early. | I do not have to get up early. | Do I have to get up early? |
he, she, it | She has to get up early. | She does not have to get up early. | Does she have to get up early? |
2.2. had to in the Simple Past
Pronouns | Affirmative sentences | Negative sentences | Questions |
---|---|---|---|
I, he, she, it, we, you, they | I had to get up early. | I did not have to get up early. | Did I have to get up early? |
2.3. Affirmative sentences with must
Modal | Substitute | Tense |
---|---|---|
I must play football. * | I have to play football. * | Simple Present |
not possible | I had to play football. | Simple Past |
not possible | I will have to play football. |
will-future |
* see also point 3 below
2.4. Negations with must not, mustn't
Modal | Substitute | Tense |
---|---|---|
I must not play football. | I am not allowed to play football. |
Simple Present |
not possible | I was not allowed to play football. |
Simple Past |
not possible | I will not be allowed to play football. | will-future |
2.5. Negations with need not, needn't, don't need, don't have to
Modal | Substitute | Tense |
---|---|---|
I need not play football. |
I do not have to play football. | Simple Present |
I do not need to play football. | ||
not possible | I did not have to play football. | Simple Past |
I did not need to play football. | ||
not possible | I will not have to play football. | will-future |
I will not need to play football. |
2.6. Questions with need and have to
Modal | Substitute | Tense |
---|---|---|
Must he play football? | Does he have to play football? | Simple Present |
Does he need to play football? | ||
The modal must is not used in the Simple Past. | Did he have to play football? | Simple Past |
Did he need to play football? | ||
The modal must is not used in the will-future. | Will he have to play football? | will-future |
Will he need to play football? |
The form need is not used as a modal, this is a main verb. This form cannot be put before another verb.
I needn't sing. (Here needn't is a modal. The main verb is sing.)
We need a new computer. (Here need is a main verb).
I need sing. (This sentence is wrong.)
3. must or have to in the Simple Present
It is not always correct to substitute have to for must in the Simple Present.
Use the modal must when the obligation comes from the speaker.
- I must go to New York. I would like to see my sister.
- You must stop smoking.
Use the modal must in written orders or instructions.
- You must log in to read your messages.
Use the substitute form have to when there is an external obligation e.g. timetable, weather or administration.
- Due to a snow storm the pilot has to land in Vancouver.
- My doctor says I have to stop smoking.