I don't feel that the three terms are mutually exclusive, though they CAN be mutually INclusive. One individual can be all three dominant, mentor AND master for one person. In fact, if a submissive's dominant ISN'T a mentor to them in one way or another, then I believe something is missing from that relationship, and more often than not, a submissive's dominant is also their master. A submissive should be constantly learning from his or her dominant, whether that dominant be Master or Mistress. On the other hand, someone who is a Master to his slave can be regarded as a dominant by other dominants or submissives, and a mentor to yet others. Dominant is, as has been stated here before, a broad term that encompasses a group of people or a way of identifying one's role within the lifestyle. Master, I believe, is a title that is earned. Much like respect. I, personally, don't require submissives or slaves to call me "Mistress" unless I have them under consideration or I own them. Though it is occasionally done by submissives who are either required to do so by the protocols set by their dominants, or as a way of distinguishing that they're speaking to me as opposed to a male that may be sitting next to me. Though I must admit that "mentor" is almost a more honored term than "Mistress" because it means that a unique symbiosis has been formed between myself the other person that does not have to be defined by our roles in the lifestyle, or even in life in general. I'm not sure if this further complicates your confusion, but I hope it helps, even if only in some small way.