Can instead of could have

[Rachel Adams]

Hello

When is it possible to use 'can' instead of 'could'?
For example:
Speaker A is looking for her bag and cannot find it. Speaker B says: ''You could have left your bag in the shop'' or ''You could leave your bag in the shop''.
Is the first option correct?

 

[Tdol]

The first option is the only one that works for me.

 

[Rachel Adams]

When should we use 'could' for an action in the past?

''I am so tired I could sleep for a week''.

''I was so tired I could sleep for a week-is wrong''. I should use 'I should have slept' but why?

 

[Rover_KE]

''I am so tired I could sleep for a week".:tick:

''I was so tired I could have slept for a week.":tick:

 

[Rachel Adams]

Thank you, Rover Ke but I need an explanation why it is wrong to say: ''you could leave your bag in the shop yesterday'', and ''I was so tired I could sleep for a week.''

 

[Rover_KE]

The word 'yesterday' refers to the past, so you need the past form 'could have left'.

'I was'tired' is the past tense so you need the past form 'could have slept'

 

[Rachel Adams]

I understand that but in this sentence: ''I listened and I could hear something'', ''I listened'' also refers to the past, however the past form of ''could have done'' wasn't used in it.

 

[Rover_KE]

That's a different meaning of 'could'. Here, it means 'was able to'.

 

[teechar]

Rachael, do you know the two uses Rover is referring to?

 

[Raymott]

Hello

When is it possible to use 'can' instead of 'could'?
For example:
Speaker A is looking for her bag and cannot find it. Speaker B says: ''You could have left your bag in the shop'' or ''You could leave your bag in the shop''.
Is the first option correct?

Your question and your title don't seem to match your example or the ensuing discussion.

 

[Rachel Adams]

So ''could'' can only be used when talking about an ability that refers to the past?

 

[Tdol]

No- it can be used for various things both present and future, but if we are talking about a past ability, we say I could swim when I was ten, not [strike]I can swim when I was ten[/strike].

 

[Rachel Adams]

No, I was asking about situations in the past. So ''could'' must be used instead of 'could have done' when it refers to an ability, eg; I could hear them. If we are talking about a possibility in the past: I can't find my bag. I could have left it in the park. In this sentence are they intechangeable or not?

I am comparing the examples given in the books I have: A Student's Grammar of the English Language Sidney Greenbaum, Randolph Quirk. It says could' can express possibility in the past. ''Her performance was the best that could be hoped for.'' My sentence: 'I could have left my bag' also expresses possibilty, that's why I don't understand why my sentence (I could leave it in the park) is wrong.
English Grammar in Use R. Murphy for actions in the past advises to use 'could have done.' Eg:'I was so tired I could have slept for a week.'

 

[teechar]

A Student's Grammar of the English Language Sidney Greenbaum, Randolph Quirk. It says could' can express possibility in the past. ''Her performance was the best that could be hoped for.''

I see your point, and I disagree with that book. I see that sentence as describing ability (not possibility). To me, that sentence means: Given the circumstances/limitations, her performance was the best that we could (were able to) hope for.

If I wanted to describe possibility for that context, I might/would/could have said, for example: "Her performance was the best that we could have hoped for".

 

[Rachel Adams]

If she performed well then we are talking about her ability to perform well and I see that you still used ''could have hoped for''.
Thus for a possibilty in the past I should always use ''could have done''. But for an ability in the past it is always 'could'. Right?

 

[teechar]

If she performed well then we are talking about her ability to perform well and I see that you still used ''could have hoped for''.

No. The verb in question is "hope". This is about our hopes, not about her performance.

Thus for a possibility in the past, I should always use ''could have done''. But for an ability in the past it is always 'could'. Right?

Broadly speaking, yes, but I generally avoid committing to absolutes. Thus, I'm not sure about "always".

 

[Rachel Adams]

''I was so tired, I could have slept for a week'', also expresses a possibility that's why using ''could'' was wrong.
Another disagreement between the two books: Murphy says if something is possible now or in the future, use ''could''. Eg: ''The phone is ringing. It could be Tom''. Not 'can' be Tom.
The second book says:for possibility use 'can'. Eg: If it's raining tomorrow , the sports can take place indoors.(It will be possible for the sports to...)
Do you agree with the book?

 

[teechar]

The second book says:for possibility use 'can'....Do you agree with the book?

Yes, but does it preclude the use "of could" for present/future possibility?

 

[Rachel Adams]

It says:

Can/could
and under ''possibilty'' lists the following examples:
Even expert drivers can make mistakes.
Her performance...(the example we already discussed)
and the last example about sports.

If 'can' can be used in the sentence: 'the phone is ringing' it can/could be Tom... why doesn't Murphy mention that? Murphy's textbook says only 'could' can be used.

 

[Rachel Adams]

So the two sentences taken from the two books express the same idea that something is possible now/in the future. ''If it's raining tomorrow, the sports could take place indoors''.
''The phone is ringing. It could be Tom''. In both sentences the correct option is ''could'' not ''can''. Am I right?