Should I feel obligated to include my advisor as coauthor? I've been working on a project with a faculty member (let's call him S) that is not my advisor (let's call him A).
They are in different departments, and have little overlap. I am working on something with S (actually I am doing it mostly by myself, with a bit of advice from S) and am planning on publishing the results. I have shared the project with A, but since it's not his field, I know he has at best a vague understanding of the contents of the paper. However he did give the idea for the methodology, which I used.
S has continued giving me advice about this paper, mostly relating to expanding on the theory of the methodology he suggested. I don't think it's very useful (he doesn't understand the context) and would prefer to just go in the direction set with S.
However, when it comes to authorship, should I include A? It feels wrong to not include him when he has been giving well-intentioned advice (and supplied a crucial suggestion for the methodology). However, it also doesn't feel right to include him, since he isn't familiar with the rest of the contents of the paper beyond the methodology section.
I am a mathematician, but I did co-author a paper published in a chemistry journal. The paper was co-authored by seven people from the lab where I worked at the time:  two mathematicians, two physicists, two chemists and an engineer (the lab director). I understood (and still understand) only the math part of the paper, I am sure that non-mathematicians, including the lab director, do not understand the math part. Nevertheless, certainly, there were no objections to including all seven people as co-authors.