What is the grammatical application for: 'I can't see the forest for the trees'?
'For' is correct. I would say it is an idiom.
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 Jacko's reply was promoted to an answer.
yes, and an idiom. But there is sth with it. For should be from. It still doesn't sound right.
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 Woodward's reply was promoted to an answer.
I think we're going with idiom!