MODAL VERBS

may/might

must/mustn't

need/needn't

should/ought to

shall/will

be able to

can/could

have to

both is used for giving advice, opinions

should

  • express necessity
  • lower level than "must"

ought to

  • same as "should"
  • higher level than "should" but lower level than "must"
  • describe the necessity of doing something right in the rules

both is used for describing what might happen but not sure about that

may

  • describe something can happen in the present

might

  • describe something can happen in the past
  • lower level than "may"

both is used for making a decision at the time of speaking

shall

  • asking for permission, giving suggestions
  • offering to help someone

will

  • describing, guessing the thing that will happen
  • offering that someone will help

must

  • describe necessity of doing something (perceive it yourself)

mustn't

  • to say that is strictly banned
  • describe probability
  • describe possible things can do by trying

"need" is both normal verb and modal verb.

normal verb

needs auxiliaries in negative and question sentences

verbs come after "need" have to be in form "to infinitive"

modal verb

only available in present form

has all the characteristics of a modal verb

needn't

  • means "not necessary"

both is used in questions of request, permission

can

  • describe the present or future possibility that a person can do something, or an event that may happen

could

  • describe the past possibility that a person can do or something, or an event that may happen