MikeNewYork
Why is it incorrect? I want to know the reason.
- Tell me the reason which you won't come.
Please let me try to divide the sentence into two to explain the matter. They would be something like this:
Tell me the reason. You won't come [for
the reason].
If you wish to join the two sentences using a relative pronoun, it goes like this:
1. Tell me the reason [for
which] you won't come.
Those words in brackets function adverbially, and therefore it's grammatically possible to use a relative adverb 'why' as a replacement:
2. Tell me the reason [why] you won't come.
However, 'the reason' and 'why' mean the same thing, so (I think) people prefer to use 'that' instead of 'why' or to use either of those words - not both of them:
3. Tell me the reason that you won't come.
4. Tell me the reason you won't come.
5. Tell me why you won't come.
#1 and #2 are grammatically correct, but unfortunately they might sound too formal or unnatural.
Well, I hope I'm not talking nonsense!