Must – English Modal Verb

The modal verb must has only one form

Must can express the following meanings:

• Duty, obligation, necessity
  • All applicants must fill in this form
  • Must he do it himself?
• Obligations expressed by must refer to the present or future but in reported speech they may refer to the past:
  • She said she must invite her friend to dinner.

NOTE: The necessity in the past is expressed with the help of its equivalents to have and to be

• • She had to see a doctor. (necessity due to some circumstances)
  • They were to meet at 5. (necessity due to a plan)
• The lack of necessity is expressed with the help of needn’t.
  • Must I phone him tonight?
  • No, you mustn’t. (It is wrong or forbidden to phone him)
  • No, you needn’t. (It is not necessary to phone him
• Prohibition
  • You mustn’t touch the statues
• Deduction – Sure that something is true (Certainty)
  • Dan must be home. I heard a noise coming from his room
• Probability (in affirmative sentences). In this meaning must can be followed by different forms of the infinitive
  • He must be thirty
  • They must have missed the bus