Language: grammar and vocabulary
Modal verbs
Choose the modal verb that carries the right meaning — ability, permission, obligation, advice or possibility.
A modal verb never works alone. It sits in front of a plain verb and colours it: can swim, must sign, should rest. What the modal adds is the writer's attitude — whether the action is possible, allowed, necessary or merely a good idea.
The five jobs worth knowing
Ability: can, could. Permission: may, can, could. Obligation: must, have to. Advice: should, ought to. Possibility: may, might, could.
Must or should
Must removes the choice — a rule, a law, a real necessity. Should leaves the choice with the reader and only recommends. If you can add "but it is up to you", the sentence wants should.
Watch out
A modal is followed by the plain verb, with no -s and no to. He can swim, never he can swims or he can to swim.
Worked example
Which modal fits: "Visitors ____ remain behind the barrier at all times"?
Ask whether the visitor has a choice.
That single question separates must from should.
Have a go
Which modal shows ability?
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.