‘If you can dream it, you can do it’. – said Walt Disney. And we cannot but agree with him. Stop dreaming and learn about modal verbs!
What Disney was talking about is ‘ability’. For current or general ability we use can or can’t.
I can eat a whole pizza all by myself.
James can’t run fast.
For future ability we also use can or can’t, will/won’t be able to.
I can get you a coffee from the bakery, if you like.
Don’t worry, Emily. You’ll be able to walk next week.
You can use may, could or can when asking for permission.
May I come in?
Can I hand in the report tomorrow?
To give or refuse permission: may/may not, could/couldn’t, can/can’t.
May I come in? – Yes, you may.
Can I hand in the report tomorrow? No, you can’t. It has to be done today.
Lawmakers, police officers and overprotective mothers looove using modal verbs. Modal verbs of prohibition and obligation in particular.
Prohibition: cannot/can't, mustn't.
You mustn't eat so many sweets.
You cannot download films without paying.
Current or general obligation: must/mustn’t, have (got) to, need (to).
You have to make your bed before leaving for school.
A lack of current or general obligation: don’t have to, needn’t, don’t need to
We don’t need to come to work on Friday. The company is testing a four-day workweek.
A lack of future obligation: don’t have to/won’t have to, needn’t, don’t need to/won’t need to.
Aren’t you happy that you won’t have to wake up early for school every day?
Asking for and giving advice: should/shouldn’t, ought to/oughtn’t to, had better:
You should go to sleep earlier.
To criticise people we use can, could, might and should/shouldn't.
You shouldn’t talk to adults that way, Billy. It’s disrespectful.
You can be really noisy, you know!
Certainty is shown with the help of must or can’t, which have opposite meaning.
This must be the book dad was looking for. (I’m 100% sure it is)
This can’t be the book dad was looking for. (I’m 100% sure it isn’t)
Possibility is shown with: could, may, might (may is more common in formal language)
This might be the right street. (I’m 50% sure)