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Hello, I have a question about using if/when in a sentence with modal verb "could".
I have Michael Swan's "Practical English Usage" 2nd edition.
In the section that I've made a screenshot of the author says that we can use "could" when we want to say something about what is/was common or typical.
Is it possible to change "if" to "when" in the sentence that I pointed at with a red arrow so it will be like this "It could be quite frightening when you were alone in our big old house"?
I'm asking this because I think this sentence is "an open/real condition in the past" and means that "something sometimes happened and can be rephrased with "when" instead of "if".
Thank you beforehand for your answers.

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DVBCIs it possible to change "if" to "when" in the sentence that I pointed at with a red arrow so it will be like this "It could be quite frightening when you were alone in our big old house"?

Yes. That's fine.

CJ

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Thank you for your answer, CJ!

So this sentence is a real/open past conditional sentence, right?

Right.

CJ

Thank you again! Could you answer the last question?

"It could be quite frightening when you were alone in our big old house". Does using "when" mean that staying in a house alone occured more often compared to using "if" in a sentence?

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DVBCCould you answer the last question?

I thought I had answered all the questions you asked. I think you mean

Could you answer another question? (referring to your new question below)

DVBC"It could be quite frightening when you were alone in our big old house". Does using "when" mean that staying in a house alone occured occurred more often compared to using "if" in a sentence?

No. Neither 'when' nor 'if' imply anything about frequency.

CJ

Thank you again! Really appreciate your fast and helpful answers!
It might be stupid and not appropriate to ask the following question in this thread but is "That's fine" an alternative to "That's correct/right/"?
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DVBCIt might be stupid and not appropriate to ask ...

No comment.

DVBCis "That's fine" an alternative to "That's correct/right/"?

Yes.

CJ