Modal Verbs | Can Could May Might | English Grammar Lesson | B2-Upper Intermediate

Hello and welcome everyone to this lesson which  is based on a question that Ramen has asked me.  

And let's see what the question is. You can  see it now. He has asked: Can we always use  

'can' and 'could' interchangeably? Well, the short  answer is no, not always. They have some similar  

functions and some very different functions.  So, let's review the eight common functions of  

these two modal verbs. Right, let's get started  with the first function, which is ability. Now,  

that's the straightforward one. Most of you use  this easily and correctly. To express ability in  

the present or future, we can use 'can'. So for  example: I can speak Spanish. You can also say:  

I am able to speak Spanish. Ability in the  present. Ability for the future also 'can':  

Can you do this tomorrow? If you say this, it  means: Will you be able to do this tomorrow?  

You're asking about someone's ability to do  something. In the past for the same idea of  

ability, we use 'could'. For example: I couldn't  finish my essay yesterday. You can also say:  

I was not able to finish my essay yesterday.  That's the most common use of 'can' and 'could',  

and I think you're pretty comfortable with that.  Number two is permission. Now, for asking for  

permission you can use 'can' or 'could'. So I  can say: Can I turn up without an appointment?  

Do I have permission to do that? Or: Could I turn  up without an appointment? The only difference is  

that 'could' is more polite. When you use 'could'.  'Could' is always more polite than 'can' when you  

ask a question. Now, be careful that although in  the question when you ask for permission you can  

use either 'can' or 'could'. To give permission  or refuse permission, you only use 'can'. So,  

if it's positive: Yes you can visit us anytime you  like. And if it's negative refusing permission: No  

you can't just turn up, you need an appointment.  Right, so I think that's not too bad yet. Still  

pretty clear. But I do need to make a note here  for you that there is another modal of verb,  

which is closely related to permission, and that  is 'may'. So, you can also use 'may' to say:  

May I turn up without an appointment? Asking  for permission. And you can use the same modal  

of verb to give or refuse permission: Yes, you  may! No you may not! Now, just so that you know,  

you may also hear 'might I': Might I turn up  without an appointment? To ask for permission.  

But this is even more formal than 'may' and very  rare. I'm just pointing it out so you don't get  

surprised. Right, but probably the best one is  'could' because it's not too formal (to ask for  

permission) and it's not too friendly either.  It's in the middle. So, that's all I have to  

say for permission. Let's look at function number  three. That's a request. Obviously, it's always  

in the question form. Again, you can use 'can' or  'could': Can you print two copies of this please?  

Or: Could you print two copies of this please?  And again, like we saw before, 'could' is more  

polite. So if you are talking to someone you don't  know very well, or your relationship is with them  

formal, then use 'could'. Friends family, can is  perfectly okay. So, that's number three. Let's  

look at function number four and that is making  a suggestion. It's always in the positive form.  

And here, for making a suggestion, we can only  use 'could'. So, for example if someone says:  

Any ideas on how to save some money this month?  And you come up with a couple of ideas to present  

them, you can say: We could skip eating out or  maybe we could turn the heating down. So, you are  

making a positive suggestion using only 'could'.  Right, now we come to the fifth function, which is  

offering. Offering to do something for someone.  And that's always in the question form. And now,  

you can only use 'can' not 'could'. So,  you see someone needs help. You can say:  

Can I help you with anything or can I get you  a drink? Not 'could' in this case. Right now  

finally, well almost finally, we come to the idea  of possibility, and that's where things can get a  

little confusing. So, let's hope I can clarify it  for you. Sometimes, we want to express a general  

possibility, make a general statement about  something, a fact. In this case, for the present,  

it's only 'can' that works. For example: In this  region, the weather can suddenly change. A general  

fact. A general statement. Now, if we wanted to  express a general fact or make a statement of  

general possibility in the past, obviously we  change to 'could'. For example: In the region  

where I grew up, the weather could suddenly  change. So just bear that in mind, because once  

we look at the next function, which is expressing  a specific possibility, you notice that 'can' is  

no longer possible. That's probably the trickiest  thing to remember. That if the possibility you're  

expressing is specific to a current situation, or  a past situation, or a future situation, but it's  

specific it's not a general statement there's  a specific context, 'can' doesn't work anymore.  

You need to use 'could'. For example in the  present we can say: There's a present situation,  

a bit of danger! Watch out! Watch out! This could  be a trap! A possibility that this is a trap. Or,  

we can use it in the past: She's late! Could she  have missed the train? Is there a possibility?  

Is it possible that she has missed the train?  And also the same word 'could' for the future:  

It could rain later today. There is a possibility  (a positive possibility) that something will  

happen later. So, the point to remember here is  not to use 'can'. So, don't say things like: Watch  

out this can be a trap! Or: can she have missed  her train? Or: it can rain later today. That's  

probably the most common mistake that I hear. Keep  it to 'could'. Or, there are two other modal verbs  

you can use. So, there's a note for you. For this  particular function that you can also use 'may'  

or 'might' for a specific possibility. So, it's  possible to say: It could rain later today. It  

may rain later today. It might rain later today.  Some people kind of say well maybe the degrees of  

possibility is different. 'May' is more possible  than 'might'. I wouldn't complicate things.  

Just say if you want to express a specific  possibility, you can use any of these three  

modal verbs. But not 'can'. Now, if this specific  possibility is about something NOT happening. So,  

we have like a negative possibility. It's possible  that this will not happen, you must only use 'may  

not' or 'might not'. Don't use 'could' anymore.  So, if you want to say it is possible that it  

will not rain later today, then the only modal  verbs you can use are 'may not' and 'might not':  

It may not rain later today. Or: It might  not rain later today. And last but not least,  

now we want to express impossibility. So, it's a  bit different from what we just saw. And now you  

can use 'can't' or 'couldn't'. So, if you want to  say it is impossible that this is a trap then you  

can use either: Don't worry, this can't be a trap.  This couldn't be a trap. There is no possibility.  

Right! We can also use the the two for the past.  So for example to express that it is impossible  

that she has missed the train, we can say: I saw  her on the platform, she can't have missed the  

train. Or: she couldn't have missed the train.  I do believe that for this possibility thing,  

because that's where things get a bit complicated,  you probably need to listen to this part of the  

lesson a few times and make some notes. But  just hopefully to help a little more, I've  

made a summary of what we've just looked at. So  for ability, present and future, 'can'. For past,  

'could'. Okay, for permission, if you're asking  for permission, 'can' or 'could'. Both are okay.  

'Could' is more polite. But to refuse or give  permission only 'can'. 'Can' or 'can't'. Requests,  

both are possible. Again, 'could' is more polite  than 'can'. For a suggestion, only 'could'. For an  

offer to help to do something, only 'can'. For a  general possibility. Making a general statement,  

only 'can'. For a specific possibility,  only 'could'. And finally, for a specific  

impossibility, 'can't' or 'couldn't'. So, maybe  this little table will also be helpful to copy  

and then review. Right, so it brings us back  to the question from Ramen, which I answered  

briefly in the beginning: Can we always use 'can'  and 'could' interchangeably? As you can see,  

no not always. In fact, the only case where  we could use them fully interchangeably was  

impossibility. And the other two cases,  where one was asking for permission and  

the other one was making it request, yes we can  use them both interchangeably. But the degree of  

formality changes, so they're not exactly the  same but similar. Right, I hope this has been  

a little bit helpful to clarify the different uses  of 'can' and 'could' for you. And if you want to  

review it a few times and make some notes, that  will help you even more. I hope you've enjoyed  

this lesson. For more on this topic, click here.  Remember to also check out my complete online  

course. And don't forget to like and subscribe.  Thank you for watching, and happy studies!