I’m beginning to think my personal improv mantra is, “make it interpersonal.”
I think there is a huge difference between your roles in a scene and the relationship that you have with the person that happens to be on stage with you.
Roles are established parameters of the two characters on stage (i.e. Lawyer and client, mother and daughter, father and son, teacher and student, and etc.). By definition, it is the proper or customary function. The position one holds to another.
The relationship is personal. It is the connection to the other person that necessitates an emotional response to a situation. To me that is the piece that when absent from the scene keeps it from moving forward. It typically shows itself as two people talking about the activity and not the way they actually feel about each other. (I.e. Lawyer and client speaking about the case, teacher and student speaking about schoolwork.)
However, I have to say some roles have interpersonal components that are built into them and, when combined, two roles at the same time can equal a relationship (i.e. Lawyer and client who are also brother and sister.)