Modals

Words like can, will, may, must, and a few others are called modals. Modal auxiliary verbs help other verbs express a meaning or an idea. Some common uses of the modals are these:

　　　　　Ability: He can speak English now.

　　　　　　　　He couldn't speak English a year ago.

　　　　　　　　I'm not able to come to the game on Friday.

　　　Permission: All passengers may now board.

　　　　　　　　We can board now.

　　　Obligation: You must fasten your seat belts. (strong)

　　　　　　　　　You should pay attention.

　　　　　　　　　 (weak)

　　　　　　　　You out to pay attention.

　　　　Possibility: It may rain.

　　　　　　　　　How could I forget an import thing like that?

　　　　　　　　　He can't /must have known the result.

Meanings similar to those of the modals can often be conveyed by real verb forms:

　He has to =...must...

　　　is able to speak English. =...can...

　　　is allowed to =...may...

is supposed to =...should... (be) able to can