could vs might (for the future possibility)

Question

Could vs might(for the future possibility)

I could go there.

I might go there.

I know that these two sentences talk about less possibility to go there.

but, I can’t know their slight difference.

When you want to tell future possibilities, how do you determine to use could or might?

Here is an example sentence.

He asked me last night if you could/might be willing to talk to Margaret for him.

I saw this sentence other website. On the website, writer explained that 'could' could mean internal possibility and 'might' could mean external possibility.

Internal possibility indicates whether the person is shy, not fluent, or which is related to his ability. External possibility indicates whether there are some obstacles like that the person has no time to meet Margaret.

How do you think about that?

Answer 1

I almost completely agree with James K's answer, but I have a slight difference, so I'm posting it as a new answer

When you say "I could go there," you generally mean you are able to or that it's possible to go there. However, when you say "I might go there," that would be the situation where it's more like "I will go there if I choose to."

Answer 2

You can pretty much choose whichever one you prefer, there isn't really much difference, in context.

If you mean "It is possible because I am able, but I may choose not to" then "could" but you can also use could, might or may in contexts that don't have any meaning of ability, with the same meaning.

I could take the train to work tomorrow.

I might take the train to work tomorrow.

The first implies "if I choose to".

Hmm, the clouds are getting thick, it looks like it could rain

... it looks like it might rain.

...it looks like it may rain.

I can detect no difference in meaning.

In the "could be willing/might be willing" There is very little difference, for all practical purposes both are acceptable.

Using "could be willing" has the sense of "being able to", which "might be willing" doesn't. But neither sentence is strictly about future possibility, these are polite requests. In this particular example "might" works better. But the meaning of "Might you be willing to talk to Margaret" or "Could you talk to Margaret" are not questions about future possibility, they are tentative requests.