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Modals for Expressing Necessity and Obligation

Necessity can be expressed using modals. 

Must and have to are used to show necessity and obligation. You can also use have got to but it should only be used in casual situations.

Must and have to show that something is necessary, or required. They also show obligation. Notice how must is stronger than have to. Must could also be used to show that something is also urgent.

Have to can also be used to show that no other options are available.

  • We must get the medicine to the sick children.
  • We must hurry to catch our flight to Italy.
  • They have to take the bus to work.
  • I have to learn English to get a promotion.

Have got to is also used like have to or must. It should only be used when speaking in casual situations. Some times have is omitted. Gotta is an informal contraction used when speaking

  • I have got to go home.
  • I got to go home.
  • I gotta go home.

The past form for have to, have got to, and must is had to.

  • I had to go home.

Will have to is used for the future.

  • I will have to go home - correct
  • I will must go home - incorrect
  • I must will go home - incorrect
  • I will have got to home - incorrect