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Always I appreciate your answers. Today I made a list of the usage of Can and Could for my better understanding for English. Though, I am still getting used to with this site. Therefore, my list is not so quite neat after all. And also there must be errors for the contents. If you help and correct those of contents, I would be truly happy about it.

  1. When they are used as possibility.

    can : High positive possibility. Present tense.

    can't : High negative possibility. Present tense.

    could : Low positive possibility. Present tense.

    couldn't : Low negative possibility. Present tense.

    can have pp : High positive possibility. Past tense.

    can't have pp : High negative possibility. Past tense.

    could have pp : Low positive possibility. Past tense.

    couldn't have pp: The same meaning with "can't have pp" but more formal.

  2. When they are used as ability.

    can : Be able to.

    can't : Not be able to.

    could : Was able to. (When the context shows a past situation)

    couldn't : Wasn't able to. (When the context shows a past situation)

    can have pp : (Not used)

    can't have pp : (Not used)

    could have pp : Was able to do it but not happened. So they are sad now.

    couldn't have pp: Wasn't able to do it but somehow they managed to do it. And they are happy about it now.

Thx.

  • Your list looks pretty good to me. – Kshitij Jan 23 '18 at 3:34
  • (+1) Up-voted for the research and effort. – Nigel J Jan 23 '18 at 3:38
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Nearly. I'll try to add some usage hints and tips:

"Can" is a modal auxiliary, used to express capacity, permission and possibility. What you are doing is conjugating the verb to have with could instead of would and can instead of will. Can in this context is a modal auxiliary (helper) verb.

can't have pp : Negate, can have = future tense

If we go out to dinner, I can't have a cake because I am on a diet. (which sadly happens to be true in my case :) )

couldn't have pp: The same meaning with "can't have pp" but more formal.

Not quite, couldn't have is conditional and refers to the past. I couldn't have a cake because I was on a diet.

can have pp : (Not used)

This is simple future, I can have a salad if we go to this restaurant.

Additionally,

[my list is not so quite neat after all] - firstly your list is great, very clear. Secondly 'quite' is not commonly used with neat, I would have said "my list is not very neat"

[And also there must be errors for the contents] - Contents is usually used in a broader context, such as the contents of a book. Must is quite strong, I would have used "there may be errors in the content or the list".

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