Clasification Modal Verbs

1. Obligation

1.1. Must

1.1.1. Conviction by yourself "moral"

1.2. Have to / Had To

1.2.1. Autority impose something "rules"

2. Advice

2.1. Ought to

2.1.1. advice, own opinion, BrE

2.2. Should

2.2.1. advice, own opinion

2.3. Must

2.3.1. Strong advice

3. Possibilities

3.1. May, Might, could

3.1.1. 50% possibility

3.2. Must

3.2.1. 90% possibility

3.3. Can´t

3.3.1. There is not possibility

4. Abilities

4.1. Can

4.1.1. Present

4.2. Could

4.2.1. Past

4.3. Be able to

4.3.1. Others verbal times

5. Permission

5.1. Ask Permission

5.1.1. Can

5.1.2. Could

5.1.3. May

5.1.4. Might

5.1.5. Shall*

5.2. Give Permission

5.2.1. Can

5.2.1.1. Someone known

5.2.2. May

5.2.2.1. More polite

5.3. Have Permission

5.3.1. Can