To express positive attitude in this situation, you can/could say...

[Indigo]

Which of the two modal verbs fits best in the following sentences and why?

1) To express positive attitude in this situation, you could say...
2) To express positive attitude in this situation, you can say...

3) I heard the story yesterday. Actually, it could be true.
4) I heard the story yesterday. Actually, it can be true.

5) The rain starts to cease. The weather could change.
6) The rain starts to cease. The weather can change.

 

[emsr2d2]

Which of the two modal verbs fits best in the following sentences and why?

1) To express a positive attitude in this situation, you could say...
2) To express a positive attitude in this situation, you can say...

3) I heard the story yesterday. Actually, it could be true.
4) I heard the story yesterday. Actually, it can be true.

5) The rain starts to cease. The weather could change.
6) The rain starts to cease. The weather can change.

Did you write these sentences yourself? If not, where did you find this exercise? As you can see, there was a word missing from 1 and 2, and the underlined sentence in 5 and 6 is, though grammatically possible, so unnatural that it wouldn't be used by native speakers.

 

[teechar]

1) To express positive attitude in this situation, you could say...
2) To express positive attitude in this situation, you can say...

See the correction pointed out by emsr2d2 above. Otherwise, both are possible. "Could" is more tentative (less certain/strong) than "can".

3) I heard the story yesterday. Actually, it could be true.
4) I heard the story yesterday. Actually, it can be true.

Again, both are possible. See above.

5) The rain starts to cease. The weather could change.
6) The rain starts to cease. The weather can change.

Those are grammatical but would only work in limited contexts, such as in a novel, for example.
What scenario did you have in mind for #5 and #6?

 

[Tarheel]

I might say the rain has slowed down or the rain has stopped.

 

[Indigo]

Did you write these sentences yourself? If not, where did you find this exercise? As you can see, there was a word missing from 1 and 2, and the underlined sentence in 5 and 6 is, though grammatically possible, so unnatural that it wouldn't be used by native speakers.

Yes, myself but I am more concerned in the use of the modals here.

In all sentences I want to make a guess about something. So, when something is possible and we want to make a guess about it, we can use modal verb could. "Can" refers to the ability to do something therefore it doesn't fit well in the context.

1) To express a positive attitude in this situation, you could say...
3) I heard the story yesterday. Actually, it could be true.
5) The rain has slowed down. The weather could change.

Am I correct in my understanding?

 

[emsr2d2]

Yes, I wrote them myself but I am more concerned in about the use of the modals. here.

What do you mean by "more concerned"? Do you mean that you're concerned about the modals but you're not concerned about the other errors? If so, that's not a good way to learn. When we correct something, we do it for a good reason.

In all the sentences, I want to make a guess about something. So, When something is possible and we want to make a guess about it, we can use the modal verb "could". "Can" refers to the ability to do something. Therefore, it doesn't fit well in the context well.

You're not really guessing in any of them. You're expressing a possibility.

1) To express a positive attitude in this situation, you could say ...
3) I heard the story yesterday. Actually, it could be true. Grammatically correct but I see no need for "Actually".
5) The rain has slowed down. The weather could change. Those are both grammatical sentences but I don't understand the connection between them.

 

[Indigo]

According to some grammar explanation about modal verbs, we use "could" to talk about specific possibilities. "Can" can be used for something that is generally possible, for example:
Traffic in Bangkok can be very heavy. (general)
She could be driving back home now. (specific)

Can I use "can" to express a possibilty in the sentences 3 and 5?
3) I heard the story yesterday. It can be true.
5) The rain has slowed down. The weather can change.
To me both sentences refer to a specific possibility, therefore I would use "could" in both sentences. Am I correct? Teechar explained that both modals were possible. Can you explain why, please?

 

[Tarheel]

Say: "I heard the story yesterday. It could be true."

"The rain has slowed down. The weather can change."

Why do you think those sentences go together?

 

[Indigo]

@Tarheel

I mean they both refer to a specific possibility. So "could" should be correct for both and not "can".

You wrote: "The rain has slowed down. The weather can change.".
In my opinion, weather can change in general but the weather could change in a specific situation, just like in the sentence below.
"The rain has slowed down so the weather could change."
Is my understanding correct?

 

[Tarheel]

@Indigo No. That makes less sense than ever. The rain didn't slow down so the weather could change.

I still don't know why you think those sentences go together. (They don't.)

 

[emsr2d2]

If you said "The rain has slowed down. The weather can change", you would put the stress on "can". You'd be using the fact that the rain has slowed down as evidence that weather, generally, can change. It's a bit of redundant statement, though. Everyone knows that weather can, and does, change.

To use "could", you'd need to say something like "The rain has slowed down but the weather could change again!" You're saying that there has already been one change in the weather (the rain slowing down) but then expressing the obvious possibility that it could change again, for better or worse.

The simple fact is that a native speaker is unlikely to use either sentence. I can come up with scenarios for sentences such as these:
The rain's slowed down but the forecast says it's going to get heavier again soon.
The rain's slowed down. You never know, it might be gloriously sunny in half an hour!
The rain's slowed down but I'm not confident we'll be playing tennis in twenty minutes.
The rain's suddenly slowed down. That just goes to show that the weather can change in a heartbeat.