Hello everyone, 

Recently, a subscriber to my Youtube Channel offered a discussion about the differences between could and might and could not and might not.

Both of these can describe possibility, however, may and might indicate a possibility that seems more likely to happen. If I had to roughly pinpoint it, I would say that: 
*May / might indicate more of a 'probability', something more likely to happen 60-70%
*Can / could indicate a possibility of about 50-60%

Of course, these are only estimates. 

For example:

I may be home early. (COMMON)
I might be home early. (VERY COMMON)
I could be home early. (not very common - but not rare either)

I can be home early. (this means 'ability' and not possibility - it can mean possibility, but it is not very commonly used in that way


Avoid using could not for possibilities.

Could not is sometimes used for possibilities, but it sounds awkward sometimes. 

I may not be home in time for dinner tonight. (COMMON)

I might not be home in time for dinner tonight.

I could not be home in time for dinner tonight. 
(NOT COMMON for possibility - this sounds formal and old - it also sounds like they are talking about a past ability that could not be done).

I can not be home in time for dinner tonight. 
(this is ability only)

Could not is used for (negative) past abilities, but rarely for (negative) possibilities in the present

Watch my Youtube video on Can and Could here: 

Watch my Youtube video on May and Might here: 

( ;) 


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