Modal verbs

1. Ability

1.1. could

1.1.1. E.g. In those days we had a car, so we could travel

1.2. can

1.2.1. E.g. Natasha can play the piano

1.3. be able to

1.3.1. E.g. It's nice to be able to go to the opera

2. Permission

2.1. be allowed to

2.1.1. E.g. Passengers are allowed to take one bag onto the plane.

2.2. could

2.2.1. E.g. In the 1920s you could drive without taking a test.

2.3. may

2.3.1. E.g. You may telephone from here

2.4. can

2.4.1. E.g. Can I use your pen?

3. Possibility and certainty

3.1. must

3.1.1. E.g. She isn't answering the phone. She must be out.

3.2. might

3.2.1. E.g. Sarah might be working late tonight.

3.3. could

3.3.1. E.g. The story could be true, I suppose.

4. Necessity

4.1. must

4.1.1. E.g. You'll be leaving college soon. You must think about your future.

4.2. have to

4.2.1. E.g. Emma had to go to the dentist yesterday

4.3. mustn't

4.3.1. E.g. I mustn't forget my key, or I won't get in.

4.4. needn't

4.4.1. E.g. We needn't make sandwiches. There's a cafe.