Can and could distinctions?

Question

I think some grammar books or online help sites group the use of the modals 'can' and 'could' in categories such as 'request' and 'ability' but sometimes I htink a sentence or question doesn't neatly fall into one but possibly fall into both or possibly mixes with other categories like 'asking for something' or 'suggestion'.

Can you cateogorize this into one? I think it can be hardly done. I think it contains both the elements of 'request' and 'ability'.

Can you lift this box?

Also, would you say that when the modals 'can' and 'could' is used in request, about the only difference is that one is more polite than the other? Or does ability play a part in that too (if I can be made to understand what I am trying to say)?

Can you lift this box?
Could you lift this box?
Can you pass me the napkin?
Could you pass me the napkin?

Doll · Accepted Answer

Anonymous
Hello Anon, you suddenly reminded me why I sometimes hate modals. In most of ESL'EFL grammar books "can" is taught as a model of suggestion but for me it is only a model of ability. At least, it would be better it if were so. (I trust myself so much nowadays) The only thing I will suggest you is that do^n't try to memorize them or put them into categories if your grammar teacher doesn't want you to do so because I don't think that in real life you will not be in a dilemma like this. At least, the context will help you understand it. With simple sentences it is really difficult to figure out. And I suggest you use "can" only for ability.
Can you cateogorize this into one? I think it can be hardly done. I think it contains both the elements of 'request' and 'ability'. -Yes you are right because without context it is sometimes impossible for me to distinguish them but as I said earlier I always threat "can" as ability. (threating can? )

Can you lift this box? --- This is ability for me. If I want a help or try to reques something I would simply use "could"

Also, would you say that when the modals 'can' and 'could' is used in request, about the only difference is that one is more polite than the other?--Well, this is possible because if I not in the mood and when a guy comes and asks me "can you do this, can you do that?", I would surely find his attitude rude. In short, "could" for requests always save a grief and maybe your life. Or does ability play a part in that too (if I can be made to understand what I am trying to say)? -- I guess I made my thought clear enough.

Can you lift this box?
Could you lift this box?
Can you pass me the napkin?
Could you pass me the napkin?

CalifJim · Answer

Anonymous I think it contains both the elements of 'request' and 'ability'. ... Can you lift this box?

Yes. Both 'ability' and 'request'. Always 'ability' on the semantic level -- the meaning of the word can itself. But 'request' or 'ability' on the pragmatic level -- the meaning and implications of the entire utterance within its social context.
can

For example, if the scene is a test of strength, Can you lift this box? is a questioning of someone's ability.
But if the scene involves a need to lift a box, perhaps to be able to clean the floor under it, then Can you lift this box? is a request for help. please is often added to show that the situation is that of a request.
____

could
If the situation is that of a request, could can and often does substitute for can, as a way to soften the present time request.

Could you (please) lift this box so I can clean the floor under it?
If the situation is one where ability is in question, could cannot substitute to indicate a present time ability, but it can be used if ability in the past is intended.
Could you lift this box two months ago? No. But you can today. See how much stronger you are now!
____

CJ

Can and could distinctions?

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