Could/could've- which of the two indicates that something has no chance of happening?

Question

If there's no chance of something happening in the future, what tense do we use to indicate that?

Let's say I have a friend whom I'm not meeting tomorrow, and they call me and say "If you came over tomorrow, we could play video games.

Would this mean my friend acknowledges i have 0 chance of being there tomorrow?

Or does could imply there being a slight chance and could've would be a better indicator of acknowledging something that is not going to happen in the future, like if someone were to say, "I wish we could meet tomorrow. I know we can't. We could've gone to that restaurant you've always wanted to go"?

Answer 1

(1) If you came over tomorrow, we could play video games.

(2) If you had come over tomorrow, we could have played video games.

Short Answer

In general, you could use either (1) or (2) to express the idea, as long as there's enough context. But if you want to specifically emphasize there's a zero chance of the future event happening, you should go with (2).

Long Answer

The past tenses in (1) -- i.e., came and could -- represent a hypothetical world, which is different from a counterfactual world. It's possible that the former happens to coincide with the actual world, whereas the counterfactual world by definition cannot coincide with the actual world.

Therefore, if you use (1) it's entirely up to context whether there's any chance of the hypothetical future event of "you coming tomorrow and us playing video games". Thus, (1) is not the way to go if you'd like to emphasize the impossibility.

Now, let's assume your friend cannot sleep over at your place or visit your place two days in a row, and that for some reason you cannot play video games until tomorrow. But your friend just came over today, which means he cannot come over tomorrow.

In this scenario, there's a zero chance that your friend can come over tomorrow and you two can play video games together. And this impossibility arises from the event that your friend came over earlier today.

In order to describe the impossible hypothetical world in which your friend comes over tomorrow and you two can play video games, you need to look back at earlier today when your friend came over, which would require the perfect tenses (e.g., had come instead of came; have played instead of play) in both the if- and main clauses. Hence, (2).

Answer 2

You are looking at types of conditionals. Education First has a nice description with examples. You are using type 2 conditional, i.e., your condition is hypothetical (but doable) and the outcome is probable (and possible).

If you came tomorrow, we could play the new game together.

Notice the simple past condition and present conditional outcome.

To describe a hypothetical in the past (i.e., it never happened) and its outcome (which is now impossible), one would use a type 3 conditional:

If you had come yesterday, we could have played the new game together.

Notice the past perfect condition and perfect conditional outcome.

This is pretty clear. However, conditionals are poorly used and even more poorly taught in English-speaking worlds. This causes people to use a sentence like:

If you were here, we could just work this out on a whiteboard.

This is an impossible hypothetical. The person cannot possibly be here. However, this sentence is idiomatic and perfectly acceptable. The technically correct sentence should have been (although I could have gotten away with should be):

If you had been here, we could have just worked this out on a whiteboard.

As I said, English speakers will often use type 2 (probable conditional) instead of type 3 (impossible conditional) if the meaning is clear from context.

Answer 3

Whether (or how much) there is a chance that something might happen does not figure in the choice of verb tense.

If you came, we could go together -- we're talking about the future, it may or may not happen, so we have future tense.

If you had come, we could have (or could've) gone together -- we're talking about the past, and so use past tense.

It's too bad you're in Antarctica; if you were closer, we could have met. If you lived next door to me, we could meet more easily. Now we're talking conditionally about something very unlikely to happen; either tense is correct, 'could have' going naturally with 'were', and 'could meet' with the implied current-tense 'lived'.

So you might use one tense or the other, regardless of the likelihood of the event happening. The tense depends on other things.