Student or Learner
He is good at English.
We are not on speaking terms.
Can I use 'in" in place of at and on in the above sentences. If not, then is there any specific rule or is it a custom?
You will sometimes hear 'He is good in English (or other school subjects), but 'at' is much more common.
We don't say 'in speaking terms' – it's just not colloquial; there's no rule about it.
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Please note that a better title would have been He is good at English.
Extract from the Posting Guidelines:
'Thread titles should include all or part of the word/phrase being discussed.'