Suppose that there is a survey of people asking them their reasons for thinking or behaving a certain way. While analyzing the survey results, a researcher may discuss all the different reasons the respondents put forth, and compare reasons that were shared by multiple people. The researcher then writes:
There is a common set of reasons that are compelling.
But I have a quibble with this: the sentence starts out with the singular subject set (thus the matching there is), but surprises the reader by making that modify reasons instead of set, as clearly indicated through the use of are instead of is that would match the singular set.
Are my instincts correct? If so, what rule of grammar is this violating?
Bonus: please suggest a good title. It's hard to come up with a title when I don't know the answer, yet. I realized that "Sentence grammaticality" is not a good title, but I don't know if the current one is an improvement.