exposition

Can

Can is an auxiliary verb, a modal auxiliary verb. We use can to:

• talk about possibility and ability
• make requests
• ask for or give permission

Structure of Can

subject + can + main verb

Could

Could is an auxiliary verb, a modal auxiliary verb. We use could to:

• talk about past possibility or ability
• make requests

Structure of Could

subject + could + main verb

Be able to

• to talk about ability

Structure of Be able to

The structure of be able to is:
subject + be + able + infinitive