adjective
1
BAD : If you find my book, could you possible return it to me?
GOOD : If you find my book, could you possibly return it to me?
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Possible is an adjective: 'It's quite possible that someone picked up your bag by mistake.' 'There are several possible answers.'
Possibly is an adverb: 'I wonder if you could possibly send me some more information.' 'How could you possibly suspect your own brother of doing such a thing?'
2
BAD : It could be possible that I left the wallet back at the hotel.
GOOD : It's possible that I left the wallet back at the hotel.
BAD : I was wondering whether it could be possible to arrange another meeting.
GOOD : I was wondering whether it might be possible to arrange another meeting.
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Do not use can/could before possible . When you are talking about a past event, use it is possible : 'It's quite possible that the letter was sent to the wrong address.' When you are talking about a future event, use it may/ might be possible : 'She thinks that it may be possible to get the watch repaired.'
3
BAD : Is it possible that I come and see you tomorrow?
GOOD : Is it possible for me to come and see you tomorrow?
BAD : She asked me if it was possible that you ring her back after 5 p.m.
GOOD : She asked me if it was possible for you to ring her back after 5 p.m.
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In enquiries and polite requests, use possible (for sb) to do sth (NOT possible that): 'Would it be possible for me to open a bank account?'
Compare: 'It's quite possible that they've got stuck in a traffic jam.'