For a paper with coauthors, what should I do if one coauthor, who I feel has contributed the most among my coauthors, declined to be listed as a coauthor and wished only to be acknowledged in the acknowledgements? The reason he gave for declining was that he did not think he has contributed significantly. The other coauthors knew this, but didn't say anything.
This happened once in the past, and at that time I did as requested by the coauthor, i.e. I removed his name from the list of authors and acknowledged him instead. The other coauthors still had their names as authors of the paper. I felt uneasy about it because I didn't think that it was right. I mean, if my second author did not think that he had contributed enough, why should the third and fourth authors stay? Of course the reader wouldn't know this, but I knew, and my third and fourth authors knew.
Now I am facing the same situation again.