Must, May, Should, Can, Could
Modal verbs that do not require the preposition “to” (must, may, might, should, can, could), can be used in the negative simply by adding “not”. To formulate a sentence using modal verbs in the negative, we use the modal verb + not + verb in the infinitive.
You may not go outside in the rain! (no contraction)
She could not remember. (couldn’t)
We must not forget the appointment next week! (mustn’t)
I should not eat so much candy. (shouldn’t)
Have to, Need to
Modal verbs that require the use of “to” in between them and the verb in the infinitive, also require the use of “to do” in order to use them in the negative. To use “have to” and “need to” in the negative, “to do” is conjugated based on the personal pronoun.
I do not need to call the office today.
You do not have to remember all this for the test.
She does not have to accept this charge.
They do not need to order food.
To formulate questions using modal verbs with “to”, (have to, need to), we continue the use of “to do”.
Depending on whether or not we use the contracted form, questions in the negative follow the same order.
Do I not have to play? / Don’t I have to play?
Do you not have to go to school today? / Don’t you have to go to school today?
Does she not need to give notice? / Doesn’t she need to give notice?