The Modals

1. Ability

1.1. can

1.2. could

1.3. be able to

2. Probability

2.1. may

2.2. might

3. Advice

3.1. should

3.2. ought to

4. Certainty/possibility

4.1. must

5. Certainty/impossibility

5.1. can't

6. Obligation

6.1. must

6.2. have to

6.3. need to

7. Lack of obligation

7.1. don't/doesn't have to

7.2. needn't

8. Polite request

8.1. May

8.2. Could

9. Prohibition

9.1. mustn't