The formal establishment of your committee usually happens simultaneously with the university's official approval of your proposed dissertation research. (This document is typically called your "dissertation proposaL") In the time between completing your courses and having an approved dissertation proposal you will work with faculty who are likely to become the officially designated committee. You may consider them your "unofficial" or your "proposed" committee for the time being. But they are not yet your official committee. There are no temporary titles which are generally used around the university, so we will use the terms "chair" and "reader," understanding that these are potential roles and titles which may change in the process of developing your dissertation proposal.