Correct Use of CAN and COULD | What's the Difference? | Modal Verbs in English Grammar

Hello there.

You know, I get this question all the time – both from my students in my classes and

on YouTube – what is the difference between ‘can’ and ‘could’?

Well, in this lesson, I will teach you the three main differences between these modal

verbs and I’ll show you how to use them correctly without making mistakes.

As always, there is a quiz at the end of the video to test your understanding.

The very first thing you should know is the basic use of ‘can’.

This verb is used to show ability.

Here are some examples: I can play the guitar.

He can lift heavy weights.

She can beat anyone at chess!

So, all of these express ability.

What about what ‘could’ then?

Well, ‘could’ is just the past tense of can.

I can say: I could play the guitar when I was in school.

That means, I had the ability in the past, but now I can’t play the guitar because

it’s been a long time and I’m out of practice.

Here a couple more examples: He could lift heavy weights until he had the accident.

She could beat anyone at chess in her prime!

‘In her prime’ means in her best years.

Maybe when she was younger and was playing competitively.

So in these sentences – ‘can’ shows present ability, and ‘could’ shows past

ability.

This is the first difference between the two words.

The second difference is when we want to talk about possibility.

To talk about what is possible, we normally use ‘could’ and not ‘can’.

Now, imagine that you and me, we’re both waiting for a train at a train station.

It’s time for the train to arrive but we don’t see it.

So I might say: Hmm, the train could be late.

So I’m making a guess about the current (or the present) situation, saying what is

possible.

Here’s another one: If you don’t study, you could fail the exam.

Are you sure to fail the exam?

No.

You could pass.

But I’m saying that it’s possible that if you don’t study, you’ll fail.

Notice that this sentence talks about future possibility.

Ah, but I have a question – we just talked about present and future possibility.

Can we talk about past possibility?

Yes, we can.

Here’s an example: Robert could have gotten the job if he had gone to the interview.

So what do we understand from that?

Well, there was a job interview.

It was possible for Robert to go to the interview and get the job.

But he didn’t go.

So he didn’t get the job.

Now, as I said before, we use ‘could’ in all these sentences to talk about what’s

possible in the past, present, and future, but there is one situation where you can use

‘can’ and that is when you want to talk about general possibility.

For example: You can catch a cold if you go out in the rain.

Traveling across Europe can be quite expensive.

You can see that these are just general statements about what is possible in the world.

In this case, it’s OK to use ‘can’, but this use is less common.

Normally, when we talk about possibility in our lives we use ‘could’.

Remember that.

Alright, let’s now move on to the final use of ‘can’ and ‘could’, and this

is in polite expressions when we talk to people.

There are four situations you need to know about.

The first is making suggestions.

For this purpose, we use ‘could’.

Here are some examples: We could try that new Italian restaurant tonight.

You could ask your sister to lend you some money.

In the first sentence, I’m making a suggestion about where we can have dinner.

In the second, I’m suggesting that if you need money, why don’t you ask your sister?

Using ‘could’ just makes it very polite.

The second situation is making requests.

Here, both ‘can’ and ‘could’ are possible: Can you pass me the salt?

Could you pass me the salt, please?

Or on the phone: Can I speak to Rahul?

Could I speak to Rahul, please?

Did you notice that I said ‘please’ at the end of the sentences with ‘could’?

That’s because ‘could’ is more polite than ‘can’.

So if you are in a formal situation, like if you’re talking to your boss or other

superior and you want to be very polite, use ‘could’.

If you’re with friends or family, then ‘can’ is fine.

Our next function is making offers: Can I get you something to drink?

Could I get you something to drink, sir?

Can I help you with that?

Could I help you with that, madam?

Again, notice the extra politeness with ‘could’.

Finally, the last conversational situation is when we want to ask for permission.

Here are some sentences: Can I borrow your pen?

Could I borrow your pen, please?

Can I take the day off tomorrow?

Could I take the day off tomorrow?

If you’re very friendly with your boss at work, you would use ‘can’, but if your

boss is very strict, then you would use ‘could’.

OK, if you’re ready, it’s now time for the quiz to see if you can use ‘can’ and

‘could’ correctly.

On the screen, there are eight sentences.

In each one, I want you to fill in the gap with ‘can’ or ‘could’.

Stop the video, think about your answers, then play the video again and check.

OK, here are the answers.

How many did you get right?

Let me know in the comments section below.

If you have any questions about these, you can ask me in the comments as well.

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Happy learning and I will see you in another lesson soon.