Modals
As Swan (Practical English Usage (Oxford University Press, 1997)), explains:
"One (of the meanings of modal verbs) is to do with degrees of certainty: modal verbs can be used to say for instance that a situation is certain, probable, possible or impossible. " p. 334
Examples:
You have to have a passport when you travel to the USA. (necessary)
You don't have to have a passport to travel to Bahia. (not necessary)
You can get married at the age of 21 (allowed / possible) but you can't get married earlier. (not allowed / not possible)
You should look after your clothes. (advisable)
You shouldn't walk alone at night. (not advisable)
(Most of the links cited below have more than these three modals. You may either read / practice only about them or about all of them. And this would be a bit more challenging! :-)
1. Uses
2. Uses
3. Uses and Exercises (print)
4. Uses and Exercises (can)
5. Uses and Exercises (must/have to/need)
6. Exercise
7. Exercise (Can/Can't)
8. Exercise (Can)
9. Exercise
10. Exercise
11. Exercise
12. Exercise
13. Game
14. Exercise
15. Uses (can)
16. Uses (must / have to)
17. Uses (should)
18. Exercise (could)
19. Exercise (mustn't / don't have to)
20. Speculations About the Past
21. Exercise
22. Exercise (present & past)
23. Exercise (present & past)
24. Exercise (present & past)
25. Exercise (present & past)
27. Song - The day before you came
28. Implied Meaning of Past Modals
29. Use of "should have / should not have"
30. Use of "must have / must not have"
31. Use of "may have / may not have"
33. Past Modals - Class activity - Teacher's notes