Easy way to understand modal verbs in English quickly

Hi guys,let us continue the lesson of modal verbs,now with the used of each modal verbs ( Can,Could,May,Might)

let's starting with Can.let as put this question :) How to use modal verbs in English ? and let's start by :

I - Usage of Can.

1- To express an ability or lack of ability in present or future.

for example :

• I can see you at 5:00 p.m tomorrow.Can you manage that ?
• They can not (can't) dance.
  

1.1- Giving or not giving permission.

for example :

•  You can use my office.
• You can not (can't) still here.

II - Usage of Could.

2- Ability or lack of ability but in the past .
for example :

• I could read without glasses last year.
• I could not (couldn't) read last day.

2.2- The second common usage of could is for making a request ( always in the question form )

for example :

• Could you repeat that please ? 
• Could we have break please ?

2.3- The third usage of could is making a suggestion ( Only in the affirmative ) 

for example :

•  what do you suggest to have for lunch ?
• We could have BBQ.

III - Usage of May.

 1- we use may to ask for permission.

for example :

• May I use your pen ?
• May we have a look ?

and remind you !
to get permission or not to get permission we use can as we just saw.

1.1- The second usage of may is to indicate a strong possibility in the present or future.

for example :

• It may happen again.
• She may not accept his offer.

 IV - Usage of Might.
1- Might it also use to express a possibility in the present or future
for example :

• It might happen again.

We can also say. ( It could happen again.) but may and might are more common for possibilities.

• She might not accept the offer.  

We do not use could in the negative for possibility  
1-1- the second usage of might is a possibility in the past ( follow by 'have done' )
 for example :

• He might have missed his bus.

We can also use could.He could have missed his bus.(but not at the negative)
I might not have managed to convince her.

Note :

'may' can also used to show a possibility in the past,but it less common than might and could :

he might/could/ (may) have missed his bus.

However,you must avoid using 'may' in a third  conditional sentence :

If i had worked hard,I would/might/could/may have passed my test.

One more thing ...
Overusing 'Can'
In very informal contexts,we tend to use 'can' instead of the appropriate modal verb.Although this is acceptable,it is always best to use the correct modal verb in formal situations and exams :
Let's look at some examples :

•  Request : Can you open the window ?

the correct modal is : Could you open the window ?

• Asking for permission : Can i use the phone ?

the correct modal is : May i use the phone ? 

• Suggestion : We can meet next year.

 the correct modal is : We could meet next year.
Possibility in present or future : It can happen again.
 the correct modal is : It might/may/could happen again.