You're too short. You couldn't dunk.

[user_user]

Talking about the present:
1. "You're too short. You can't (almost 100% disbelief) dunk." vs. "You're too short. You couldn't (8-90% disbelief) dunk."

Talking about the future:

2. "He can't (100% certain) come tomorrow." vs. "He couldn't (8-90% certain) come tomorrow."

Is my understanding about the percentage correct? And you can use "couldn't" to talk about both the present and future as above, right?

 

[Tarheel]

I don't know what you're talking about.

You can certainly use "could" or "couldn't" to talk about the past.

 

[user_user]

I don't know what you're talking about.

You can certainly use "could" or "couldn't" to talk about the past.

could=was able to. I already know this. That's not what I'm talking about.

"Could" can be used to talk about the present and future, right? What I'm asking about is its negative form.

(examples below are made up by me)

Talking about the present:

1) You can lift this weight. vs. 2) You could lift this weight.

I say 1) when i'm almost 100% sure you can lift this weight.
I say 2) when i'm less than 100% sure you can lift this weight. (but more certain than might)
Or am i misunderstanding about the usage of "could"? 2) can only mean something like a hypothetical situation, "You could lift this weight if you tried"?
Doesn't "could" in 2) have a somewhat similar meaning to "might or would be able to"?

Talking about the future:
Doesn't "he couldn't come tomorrow" mean something like "he wouldn't be able to come tomrrow"?

 

[jutfrank]

Is my understanding about the percentage correct?

No. I think you've got it completely wrong.

Let's deal with just one example at a time.

 

[Tarheel]

How would I use "could" in real life? (See below.)

I could do that ten years ago. Now it is not easy.

"I could do that if I wanted to" is certainly possible. In this case, of course, the person is talking about a hypothetical situation.

 

[user_user]

No. I think you've got it completely wrong.

Let's deal with just one example at a time.

What do you mean completely wrong??
I've looked up the dictionary and they are mostly right.
The percentage actually should be equal (only 10-20% difference).
The point was right, can't=couldn't; both used for a present or future impossibility.

What do you mean completely wrong??
Maybe you're talking about ability vs. possibility?
'Couldn't' is not used for ability (present + future), but only for possibility (present +future in an impossibility sense)?
Like dunk is about ability, so i should say like 'won't be able to dunk' instead of 'couldn't dunk'?? even that is a minor issue.

Anyways, no comments have been helpful in any way so far, and by now I'm almost getting my answer by myself through dictionaries and chatgpt so.

 

[Tarheel]

Say:

I looked it up in the dictionary....

I fail to see your point. "Can" and "could" do not mean the same thing. Neither do "can't" and "couldn't". What are you trying to say?

 

[emsr2d2]

We've had multiple threads on the forum in which learners have tried to get us to apportion percentages of possibility/probability to words such as "could", "might" etc. We will not do it. Context is always important and dictates what is probably meant.

 

[jutfrank]

What do you mean completely wrong??

I mean that in my opinion the very idea that these words have anything to do with degrees of possibility is completely wrong.

I've looked up the dictionary and they are mostly right.

No, I think that not only are those numbers kind of silly, the whole idea of giving numbers is based on a misunderstanding in the first place.

The percentage actually should be equal (only 10-20% difference).

No, that's silly.

Maybe you're talking about ability vs. possibility?

Yes, exactly.

'Couldn't' is not used for ability (present + future), but only for possibility (present +future in an impossibility sense)?

If I understand you correctly, then yes, I agree with that.

Like dunk is about ability, so i should say like 'won't be able to dunk' instead of 'couldn't dunk'?? even that is a minor issue.

I'm going to guess what you mean:

You're too short. You can't dunk.

This is about ability. In other words, it means that there is zero possibility of you dunking now, or in the past, or in the future, because you lack the height to do so.

Anyways, no comments have been helpful in any way so far, and by now I'm almost getting my answer by myself through dictionaries and chatgpt so.

Good luck with that. If you want us to help you understand this very difficult topic, then let's stick to one example at a time.