Can and could

Can and could are modal auxiliary verbs. Let’s look at why we use two, very similar modal auxiliaries, can and could in English.

We use can and could to talk about ability, be it in general or present ability 

• I can ride a bike.
• When I was five I could ride a bike. (‘could’ functions as the past of ‘can’ as well as having its own meaning).
• She can do what she wants, it’s none of my business.

We use could to talk about the past when referring to something that happened on only one occasion

• When she was young she could drink what she liked.
• James could smell the fish.

The form be able to is used to express ability or capability in the future 

• By next week I’ll be able to drive on my own with an adult.
• She’ll be able to come to the meeting next week.

We use can and could to express probability and possibility

• Can you let me know what you’re thinking about doing?
• I could go to the concert tonight, but I’m really not sure.

We use can and could for interpersonal uses, such as in requesting, asking questions, permission etc.

• Could you please let me know where I need to go to get to Madrid?
• Can I offer you something, sir?
• You cannot cross the road! it’s a red light.

We use can and could to express ability or perception with verbs such as see, taste, feel, hear, smell etc.

• Yesterday, at the conference I couldn’t hear the speaker.
• I can see and feel just fine doctor.
• Can you please taste my meal and tell me what you think?

See also