Can vs. Could

can could modals

'Can' and 'could' are two of the most commonly known modal verbs. In this lesson, we will learn their differences and when to use each of them.

"Can" vs. "Could" in the English grammar

What Is Their Main Difference?

The main difference between modal verbs 'can' and 'could' is that 'can' is in the present tense but 'could' is in the past tense.

'Can' is one of the most commonly known modal verbs. It helps us talk about abilities, ask for permission, request something, offer things, etc. We use can refer to the present and the future. Have a look:

I can wash the dishes.

I can pick you up tomorrow.

'Could' is also another well-known modal verb. To put it simply, 'could' is the past tense of 'can.' Like 'can,' it is used to talk about abilities, request something, etc. For example:

I could buy a car.

I could reserve a table.

Similarities

Talking about Abilities

We use 'can' and 'could' to talk about abilities that derive from knowledge or talent or general skills. 'Can' is used to talk about the present and the future but 'could' is used to talk about the past. Have a look:

I can speak three languages.

I could run fast before I broke my left.

Talking about Possibilities

When we want to talk about possibilities in the past and the future. While 'can' expresses a high probability, 'could' suggests a lower chance of possibility. Watch:

Unhealthy food can cause cancer.

Crime could be prevented by this program.

Talking about Permission

'Can' and 'could' are used to ask for or to give permission for something. When asking for permission, 'could' is politer and more formal than 'can.' For example:

Can I use your phone?

Here, we are asking for permission.

Could I use your phone?

Here, we are asking for permission.

You can use my phone if you like.

Here, we are giving permission.

You could always use my phone.

Here, we are giving permission.

Requesting

The modal verbs 'can' and 'could' are used in question form to ask someone to do something. In this context, 'can' is informal. In formal occasions, use 'could' as it is more formal and politer. For instance:

Can you pour me a glass of water?

Could you pour me a glass of water?

Negation and Question

'Can' and 'could' are used in negative sentences. They are turned negative by being attached to a 'not.' You can see the process below:

Can → Cannot
Could → Could not

'Cannot' and 'could not' also are contracted as shown below:

Cannot → Can't
Could not → Couldn't

I can't attend the wedding.

I was sick, so I couldn't drive.

As modal verbs, 'can' and 'could' are used to create questions through inversion. For example:

Can I pass this exam?

Could you help me with my homework?

Differences

Talking about Facts

We use 'can' to talk about general or scientific facts, but we cannot use 'could' to state facts as facts are always true and perhaps never cease to be accurate. Have a look:

Sharks can live up to 30 years.

Elephants cannot jump.

We use 'could' to talk about historical facts or facts that were true in the past. For example:

Loki could change his appearance.

Loki is a character in Norse mythology that does not exist anymore.

The Elephant Man could only walk with the aid of walking sticks.

Talking about Potential

Potential is currently unrealized ability. We use 'can' to show the potential in a person or something. Have a look:

This artwork can win the prize.

We use 'could' to talk about lost causes and missed potentials which (if taken advantage of) could have been great opportunities. Watch:

This artwork could win the prize.

With Conditionals

'Can' is used with conditional type 1, which talks about an absolute promise. However, 'could' talks about a situation with a chance of occurrence, and therefore, it is used with conditional type 2. Have a look:

If you promise to be careful, you can drive my car.

If I had 600$, I could buy that Snowboard.