Need (to) / Must / Have to

    Affirmative

  • MUST usually expresses OBLIGATION:

    • You must use a dictionary for this exercise, please check the spelling.
    You must study the irregular verbs for next week.
    (= It is obligatory.)

  • NEED TO expresses NECESSITY:

    • You need to use a dictionary for this exercise, it has many new words.
    We need to study the irregular verbs, the teacher will include a question in the exam.
    (= It is necessary.)

  • HAVE TO can express NECESSITY or OBLIGATION:

    • We have to use a dictionary for this exercise, the teacher said we have to check the spelling.
    (= It is necessary to use the dictionary, it is obligatory to check the spelling.)
    We have to study the irregular verbs, the teacher will include a question in the exam.
    (= It is necessary to study them, it is obligatory to revise for the exam.)

    Negative

  • MUST NOT expresses PROHIBITION:

    • You must not use a dictionary when you do this exercise.
    You mustn't study today, the doctor said.
    (= It is forbidden.)

  • DO/DOES NOT NEED TO / NEED NOT and DO/DOES NOT HAVE TO express ABSENCE OF NECESSITY or ABSENCE OF OBLIGATION:

    • You don't need to use a dictionary when you do this exercise.
    You needn't study the irregular verbs for tomorrow's exam.
    (= It is not necessary.)

    You don't have to use a dictionary when you do this exercise.
    You don't have to study the irregular verbs for tomorrow's exam.
    (= It is not obligatory / it is not necessary.)