How to use the word "can"

Question

Hellow teachers, I'm not quite clear about the usage of the word can, it has the meaning of one's ability to do something, e.g. I can see her sitting there in the bar; and it also means there're chances/possibities that some events may happen, e.g. That couldn't be her, she is still on her vacation in L.A.

Here's the question, is it okay to say this? She is still on her vacation in L.A., you couldn't see her at the bar.
Apprently the sentence means that it's impossible for you to see her at the bar because she is on her vacation in L.A.
Some may say it this way, She is still on her vacation in L.A. you can't have seen her at the bar. Is this correct?
I'm not sure if my conclusion is right, my view is that Can or Could would only have the meaning of chances or possibilities when it's followed by the link verb be. Am I right?

All advices are welcomed, thanks a lot!

Terryxpress · Accepted Answer

She is still on her vacation in L.A., so you can't have seen her at the bar.
Here, the speaker is totally confident in making this assertion, and the other person has made a mistake.

But
She is still on vacation in L.A., so you couldn't have seen her at the bar.
Here, the speaker still asserts that it seems impossible, and the other person has made a mistake, but also acknowledges that he, the speaker, might be mistaken. It is as if the sentence could be something like this:
She is still on vacation in L.A., so you couldn't have seen her at the bar - unless...unless I've got the dates mixed up and she's back already.
Note the change in tense. The sense of the statement is that someone said:
"I saw Mary at the hotel bar last night", and the speaker is replying to this.

RobinG · Answer

Thanks Terryxpress.
Okay, let's assume this is the scenario:
A:I saw Mary at the hotel bar last night.
B:___________.(will the 2 sentences both fit here?)
1.You couldn't have seen her there, she is still on vacation in L.A.
2.You couldn't see her there, she is still on vacation in L.A.
If we can say: 1.You couldn't have seen her there, she is still on vacation in L.A. then dose it make sense to say 2.You couldn't see her there, she is still on vacation in L.A. (it soulds strange, but does it make any sense at all?)
I know the "couldn't" in the 2nd sentence has the sense of the ability to do something, e.g. you weren't able to see her.....But in the 1st sentence I think it has more sense of the chances/possibilities of some situation than the ability to do something. Is it because of the different tense that the same word is being given a different meaning? I hope I've made my point clear.

Terryxpress · Answer

Checking my email and saw you had posted. It's getting late here, so will answer tomorrow. Interesting (and answerable) questions!<img class='emoticon' style='Width:19px;Height:19px;' data-delaysrc='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/1.gif' src='https://uat-englishforward-forums-backend.s3.us-west-2.amazonaws.com/Emoticons/1.gif' alt='Emotion: smile'/>

RobinG · Answer

Hi Terry, looking forward to it.

Terryxpress · Answer

Back with you.

Grammar books will give half a dozen ‘uses’ of the Present Tense, as in ‘to talk of time-tables and schedules’ and ‘when referring to future plans that are definite etc.

The reason why this is possible, is because fundamentally, the Present Tense asserts a FACT, which is true (even if expressed in the negative):
He is a plumber.
I am not a liar.

Similarly, the Past Tense states a FACT:
He died.
He ate all the pie.

Further, the situation/events referred to are complete, finished, over and done. That being the case, then there is no room for speculation – the outcome of those events is a FACT, as in “He died.”

‘could’ is used as the Past Tense of ‘can’:
These are great seats. I can see everything
I can’t see anything without my glasses.
Past Tense:
We had great seats. I could see everything.
We went to a rock concert last night. I couldn’t see the performers for all the fans standing and waving their arms in the air.
Note the factual nature of these: ‘could see’ or ‘couldn’t see’

The modals allow us to speculate, to imagine possible outcomes, to talk about unreal, unrealized, and imaginary situations.

So – let’s look at your sentences:
I saw Mary at the hotel bar last night.
The gist of your reply is that that is not possible because she is out of town, in LA, as in:
She is still on vacation in L.A., so you couldn’t…………
The conversation has moved from assertion of a Past Tense FACT – I saw her – into the realms of ‘possibility’.
On the one hand, you are saying that, of the two possibilities (a) ‘he saw her’, and (b) ‘he didn’t see her’, you contend that it is not possible for this to have occurred;, but then want to use the Past Tense, which would indicate that you accept what he said as a FACT, that it really DID happen.

We can’t use the Past Tense verb form to talk about whether something possibly happened or not!

Hope that helps.

CalifJim · Answer

RobinGShe is still on her vacation in L.A. You couldn't see her at the bar.

No. You want You can't see her at the bar. ~ It [is / will be] (physically) impossible to find her at the bar.
Or You [can't / couldn't] have seen her at the bar. ~ It's (logically) impossible that you saw her at the bar.

What you have is: You couldn't see her at the bar. ~ It was impossible for you to see her at the bar. / You failed to see her at the bar. (The sentence is correct, but it has no relationship to her being on vacation elsewhere.)

The relationships between all these modals are frustratingly asymmetric. Sometimes a combination is not used; sometimes the same combination has multiple meanings; sometimes more than one combination has the same meaning. It's a headache.

Here are some combinations illustrated with the verb "try". You can substitute other verbs, of course.

You can try. ~ It is possible for you to try. / You are permitted to try.
You can't try. ~ It is not possible for you to try. / You are not permitted to try.
You can have tried. [not used]
You can't have tried. ~ It is not possible that you (have) tried.

You could try. ~ It [would / might / may] be possible for you to try.
You couldn't try. ~ It was not possible for you to try. / You failed to try.
You could have tried. ~ It was possible for you to try. / It is possible that you (have) tried.
You couldn't have tried. ~ It was not possible for you to try. / It is not possible that you (have) tried.
________________

RobinGmy view is that Can or Could would only have the meaning of chances or possibilities when it's followed by the link verb be. Am I right?

No. Even with linking be, can and could can have meanings other than chance or possibility, even though what you say is often true.

Susan can be very talkative. ~ Susan has the potential to be very talkative. (She is often talkative.)
(This is not really exactly the same meaning as "It is possible for Susan to be very talkative".)
Only Lenny could be the leader of the group; the others were too inexperienced.
~ Only Lenny was able to be the leader ...
~ Only Lenny had the necessary qualifications to be the leader ...
(This is not the same meaning as "It might be possible for only Lenny to be the leader ...".)

CJ

RobinG · Answer

Thanks Terry for the elaborated explantions and examples, really to the point, seem to me.
But I have reservations about this take: We can’t use the Past Tense verb form to talk about whether something possibly happened or not!
What about this?~ That couldn't be true! Can we indicate that something was not possible to be true or something was not possibly true by saying this? Yeah... it's rather in the sense of something being....than something happening or taking place....
Sorry hope I'm not being pigheaded, I'm literally muddled by these possibilities, chances, and past tense and present tense......

RobinG · Answer

Thanks CJ. the physically & logically impossible thing.... is really interesting.
So as you examplified, You can't see her at the bar. ~ It [is / will be] (physically) impossible to find her at the bar.(We can assume that she is blocked from you by a pillar or something, right?)

While in this one: You couldn't see her at the bar. ~ It was impossible for you to see her at the bar. / You failed to see her at the bar.
So suppose the sentence is correct, let's put it in here, I couldn't find her at the bar yesterday because she is still out of town on vacation.~It was impossible for me to find her at the bar yesterday because she is out of town on vacation. Can I understand it this way?

Sorry seems I'm just asking question after question after question here in contradiction to your verdict.
Really appreciate your comments all the way, very helpful indeed! I've got it very clear now.Thought I might just as well buy a Webster and plough through it all.

Terryxpress · Answer

It's my fault. The statement "We can’t use the Past Tense verb form to talk about whether something possibly happened or not!" is not clear enough. Hopefully, I can make this clearer:

What about this?~ That couldn't be true! Can we indicate that something was not possible to be true or something was not possibly true by saying this?
Look at these sentences:
A: I heard that Sue and Jim have split up.
B: That can't be true. They booked to go on a holiday together just this morning. (= here and NOW, I say to you that I doubt that this is true - Present Tense)
compare
Z: John told me that Sue and Jim have split up, but I told him that couldn't be true, because...(Past Tense)
compare, from my last post:
These are lousy seats. I can't see anything. (Present Tense)
We went to a rock concert last night. I couldn’t see the performers for all the fans standing and waving their arms in the air. (Past Tense)

Let's go back to your original scenario, but change 'saw' to 'bumped into' (=met by chance) AND withhold the information that your logical deduction is based on:
A: I bumped into Mary in a bar last night.
B: You couldn't bump into her there.
YES YOU CAN! As soon as she's back in town, pop into the bar occasionally, because she often frequents that bar. THEN, it is quite likely you will bump into her! The statement has the meaning, that bar is not a place that Mary goes to!

What you are wanting to say is that last night, the 'bumping into her' didn't happen at all. You then reveal your information - she's out of town - to demonstrate why what he is telling you about is 'unreal', 'must be a figment of his imagination' .........or he's lying; and you could say:
A: I met Mary in a bar last night.
B: That can't be true - you're lying. Mary is out of town.
Here, you are challenging, right then and there, the NOW, the truth of his assertion; whereas in the original, you are saying you cannot accept the situation last night as being REAL.

Does that help?

Terryxpress · Answer

Addendum to:
A: I met Mary in a bar last night.
B: That can't be true - you're lying. Mary is out of town.

In the Past Tense that would be:
John told me he met Mary in a bar last night. I all but called him a liar to his face. I told him that couldn't be true, because Mary is out of town.

And further:
I can't run one kilometer, never mind run a 5 kilometer marathon. (Present Tense fact)

I went jogging yesterday, and couldn't even run one kilometer.(Past Tense fact)

John completed the marathon? I don't believe it. He couldn't have run the whole five kilometers (=talking about the UNREAL situation of his actually, actually, running that distance). Last time I spoke to him, he couldn't even run more than one kilometer.(talking about a REAL situation.)

How to use the word "can"

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