Modals and their meanings

can

  • general ability (present)
Ants can survive anywhere, even in space. Jorge can run a marathon faster than his brother.
  • informal requests or permission
Can you tell me where the light is? Sandy can borrow my calculator.

could

  • general ability (past)
Lea could read when she was only three years old.
  • polite, informal requests or permission
Could you give me that pen?

may

  • formal requests or permission
May I see the report? Students may park only in the yellow zone.
  • possibility
I may try to finish my homework tonight, or I may wake up early and finish it tomorrow.

might

  • possibility
Funding for the language lab might double by 2017.

note: Might usually expresses a stronger possibility than may.

must

  • necessity (present or future)
To be effective, welfare-to-work programs must provide access to job training.
  • strong probability
Amy must be nervous. [She is probably nervous.]
  • near certainty (present or past)
I must have left my wallet at home. [I almost certainly left my wallet at home.]

should

  • suggestions or advice
Diabetics should drink plenty of water every day.
  • obligations or duties
The government should protect citizens' rights.
  • expectations
The books should arrive soon. [We expect the books to arrive soon.]

will

  • certainty
If you don't leave now, you will be late for your rehearsal.
  • requests
Will you help me study for my psychology exam?
  • promises and offers
Jonah will arrange the carpool.

would

  • polite requests
Would you help me carry these books? I would like some coffee. [Would like is more polite than want.]
  • habitual or repeated actions (in the past)
Whenever Elena needed help with sewing, she would call her aunt.