words can and could

[Richard]

I pick these sentences up from a BARRON's book, which are AmE sentences:
1-Well, just try to count all the grains of sand on all the beaches on Earth. That would be about 100 billion. But of course, you couldn't even count them in your lifetime, could you?
2-he's treated you unfairly in some way that could cause you to...(something)
3-so that would be two hours a week then?
I could do that.

why not can instead of could?
what the difference between:
can you? and could you?
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[Cgk]

Hello Richard_Jack.c,

I understand the difference between can and could this way:

can is "definitely"
could is "possibly"

In sentence number 1, "could" was used because the speaker cannot be certain that his statement is correct. It is hypothetical.
In sentence number 2, "could" could also be exchanged with "might": he's treated you unfairly in some way that MIGHT cause you to...(something)

Neither of these sentences say something definite, therefore "could" was used, not "can".

To the experts: Please correct me if I'm wrong.

Claudia

[Alan]

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Hi Richard,

If you look closely at the verb form 'could', it has the idea of 'would be able to' and that is the sense in which it is used in your sentences. It gives the idea of 'probability'. 'Can' on the other hand suggests possibility. Look at these: I could meet you on Tuesday but I'm not sure exactly what my plans are (probability). I can meet you on Wednesday because I have no other plans (possibility)

Remember that 'could' can also mean 'was able to' as in: Charlie can run as fast as a rabbit. I remember I could when I was his age.

Alan
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[Cgk]

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Hello Alan,

thank you for your response.

I have a question and would appreciate you helping me out on this.

To me, "probability" and "possibility" fall into the same category. Neither of the two expresses something precise, indisputable, something that is for certain.

When I hear somebody say, "I can do it." then it sounds to me as though he is certain of it that he can do it, and that he definitely will.
When I hear somebody say, "I could do it." then it sounds to me as though he is possibly able to do it, but he probably won't.

This is why I came to the conclusion, that can is "definitely" and could is "possibly/probably". Unless, of course, as you have already mentioned, "could" is being used as the past tense of "can".

Claudia

[Alan]

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Hi Claudia,

These are fine points. I would make a distinction between what is probable and what is possible. The similarity is that they are both,as it were, unrealised - not put into practice. How I would distinguish them would be that 'possible' is to be realised and 'probable' is likely to be realized. When I say 'I can', I am just saying 'I am able' but I'm not necessarily be going to. When I say 'I could', I may well be able but it's not necessarily likely.

I don't know whether I have answered your points

Alan
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[Cgk]

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Hi Alan,

oki, I shouldn't have said "and he probably will" along with the "I can do it" example. I just wanted to whip out the word "definitely" and sound all smart, but it was thoughtless of me. Allow me to scratch that part of the sentence.

I guess what I'm trying to say is that I like to think of "can" as something certain, and "could" as a big maybe. It makes using "can" and "could" easier for me, and better to distinguish them from one another. The same goes with "will" and "would". This is why I was confused when you said that "could" gives the idea of "probability" and "can" suggests "possibility" when probability and possibility are so similar.

The way I understand it now, "can" means either definite or possible, and "could" means both probable and possible, but not definite.

Did I get it right?

Claudia

[Alan]

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Hi Claudia

Well, I don't want to flog a dead horse but to me the idea of 'I can' doesn't really mean 'definite'. To me it is purely and simply ability/possibility. And that's really the best I can do!

Alan
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[Cgk]

Thank you, Alan, for your patience and taking the time to explain. You were very helpful.

Claudia

[Kitosdad]

I can eat six shredded wheat.

I could eat twelve shredded wheat, if I was really hungry.

Certain v Possible.

Kitos.
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[Cerberus™]

Alan, to grab the dead horse by its manes and drag it along for a few more miles, what about this:

- I can do it: I have the power to do it; whether or not it will happen is my decision. Possibility.

- I could do it: the above, but in addition there is another condition that must be fulfilled, which is likely to be out of my control; that is why it is called a conditional; and that is why it is the more tentative statement. Probability.

This distinction is of course merely theoretical: in daily usage it is not always so clear. In addition there can be other reasons for using either form, such as a past situation, or a permission given.

[Alan]

Hi Cerberus,

Thanks as always for another valuable contribution.

Alan
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[Cgk]

[Alan]

Hi Claudia,

Yes you did. I was just trying to keep everyone happy.

Alan
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[Cgk]

Claudia

[Richard]

Thank you all.

I get precisely what Alan wanted to say.