The English native speaker teacher of a friend wrote the following question:
What role does reason and emotions play in sharing knowledge?
As far as I know, this question has a grammatical error, for the subject is plural: reason and emotions. So it should be:
What role do reason and emotions play in sharing knowledge?
However, I think that if his teacher had taken reason and emotions as one whole unit, then he could use does instead of do. I am not sure if that way of expressing the question would be idiomatic though. Is the usage of does possible in this case, or is it just a grammatical error?