Should someone be an author if they helped understanding a concept? I am writing a paper. I have performed the experiments and I also have the results. However, there is a section in my paper where I have to explain my observation upon which the whole idea is based. To ensure that I explain my observation correctly, I want help from a professor. I will be basically asking him questions along the line of: ‘why does this happen?’.

Before asking such questions, shall I inform him that I’m writing a paper and need help in explaining something?
I’ll definitely thank him in the acknowledgement section but is it required to add him as an author?
To ensure that I explain my observation correctly, I want help from a professor. I will be basically asking him questions along the line of: ‘why does this happen?’.


Whether this merits coauthorship depends on whether the professor is making a significant intellectual contribution.  If you are just getting straightforward explanations of well-known theory (which you need because you are an experimentalist, not a theorist), then there's no need for more than an acknowledgment.  On the other hand, if nobody knows why these things happen and the theorist comes up with a novel explanation for your data, then coauthorship sounds appropriate.  There may also be intermediate cases, such as theory that is relatively well known but requires some calculation to apply to your case, in which case you would need to discuss whether coauthorship makes sense.


  Before asking such questions, shall I inform him that I’m writing a paper and need help in explaining something?


Yes, certainly.  If you get only quick answers that do not seem to involve much effort, then you should mention the paper but there's probably no need to discuss coauthorship.  If you get answers that seem to involve serious effort, then you should discuss coauthorship.  (Discussing it doesn't necessarily mean he will be a coauthor.  Rather, you just need to be careful to make sure there are no misunderstandings.)