[Grammar] conditional sentence - "if i knew they had a problem.."

[DANAU]

I have extracted the sentence below from Practical English Usage by Swan.

"If I knew they had a problem, I could have helped them." - according to Swan, this sentence is incorrect, with reference to 241.2 in the book.

241.2
- We can use could have + past participle to mean 'would have been able to ... '
- and might have + past participle to mean 'would perhaps have ... ' or 'would possibly have ... '

I have totally no clue on why the sentence above is incorrect because it seems perfectly fine to me.
Also, the book does not suggest a correct version for this sentence as what it does for other wrong sentences.

It also seems fine to me to replace 'could have helped them' with 'would have helped them' depending on context.
But I feel both are grammatically correct. Is this the case?

Can you help to explain the rationale why Swan is saying the sentence is wrong.

 

[GoesStation]

It should begin If I had known they had a problem.

 

[DANAU]

Thanks, GoesStation.

With reference to 241.2 - 'We can use could have + past participle ... ', 'knew' is simple past while
'known' is past participle so the correct usage should be 'known'. I think I understand it now.

 

[DANAU]

The book states the usage below:
- 'if + past' is used for unreal or improbable situations now or in the future.
- 'if + past perfect' is used for unreal or improbable situations happened in the past.

I have written a few sentences below. Can you help me check if they are correct.

1. If I had known you would be joining us, I would have ordered more food. (talking to a friend while having dinner now, but ordering is in the past)
2. If I knew how high the stock price would climb, I would have more confident to invest now. (I can't tell and the time is present and looking ahead)
3. If I knew she needed money, I would have saved up for her. (this is a past event so am I right so say we should use "had known" instead of "knew"?)


I came across an excerpt below taken from the Los Angeles Time.

"I deserve a punishment for my crime ... If I knew what I know now, I wouldn't have joined the gang. It's not worth dying over a fading colour".

The sentence above is talking about a past event so my understanding is the correct usage should be "If I had known what I know now ... ". Can you explain why the writer used "knew" instead?

 

[GoesStation]

I came across an excerpt below taken from the Los Angeles Time.

"I deserve a punishment for my crime ... If I knew what I know now, I wouldn't have joined the gang. It's not worth dying over a fading colour".

The sentence above is talking about a past event so my understanding is the correct usage should be "If I had known what I know now ... ". Can you explain why the writer used "knew" instead?

Many Americans use the past simple where formal rules require the past perfect. The former gang member, who probably did not come from a highly educated family, is one of them.

 

[Rover_KE]

Many Americans use the past simple where formal rules require the past perfect.

I first heard the song If I Knew You Were Comin' I'd've Baked a Cake in 1950. Even then, at the age of 12, I knew that should have been If I'd known you were comin' ....

When I mentioned this some years ago on a forum like this, a number of AE speakers shot me down in flames saying exactly the same as GS above and telling me to mind my own business.:-?

I'll get my coat ...

... oh, wait a minute — I'm on lockdown so I'll go and wash my hands again.:roll:

EDIT: I'm not implying that GoesStation shot me down in flames or told me to MMOB.;-)