I've been thinking about roles such as being married, being a parent, being a sibling, being a second cousin, being a firefighter, being a president or being a monarch. These roles come along with moral duties, permissions and rights. Each role has entry conditions, such that when one satisfies the entry condition, one falls under the role, and some of the roles have exit conditions. In some roles the entry conditions involve one's agreeing to enter the role—marriage, firefighting, presidency and monarchy are like that—but in some the entry conditions may have nothing to do with one. On the other hand, one need not do anything to become a sibling.
Here's what I am inclined to think about such roles. Our human nature specifies what one might call natural roles. Some of our natural roles directly give us roles. Thus, I think being married and being a parent are natural roles. I am not sure about being a sibling, and I quite doubt that being a second cousin, being a firefighter and being a president are natural roles.
Roles can have sub-roles which have more specific duties, permissions and rights. These sub-roles derive all their normative force from the full role and other conditions. For instance, the role of parent has sub-roles such as: parent of a small child and parent of an adult child. The moral duties, permissions and rights associated with the sub-role derive from the moral duties, permissions and rights associated with the full role together with the fact of the satisfaction of the condition.
My big conjecture is that all roles that are not natural are sub-roles of natural roles. Thus, there is no natural role of second cousin, but there is a natural role of distant relative, perhaps. The duties, permissions and rights of being a distant relative depend on multiple conditions, including the closeness of the relationship and the operative social conventions. So there may be such a thing as the role of second cousin in mid-twentieth century rural Pennsylvania. All the moral normative oomph in this sub-role comes from the moral normative oomph of the natural role of distant relative. It does this by means of the natural role having requirements that are conditional, in this case on closeness of relationship and the social conventions in place. For instance, the natural role of distant cousin may say: "Fulfill those non-immoral conventional duties associated with your degree d of relationship whose fulfillment does not exceed degree of onerousness c(d)", where c(d) is some function setting a cap for how onerous a conventional duty one is required to fulfill in the case of a degree d of relationship (presumably the closer d is, the higher the cap). In this way, conventional duties (which on my view are no more duties in themselves than rubber ducks are ducks) become moral duties when the natural role makes them so. Thus, a conventional duty to come to second cousins' weddings yields a moral rule that one should come to second cousins' weddings, when the onerousness does not exceed c(d), where d is the degree of relationship involved in being a second cousin.
We could have cases of non-natural roles whose moral normative oomph derives from two or more natural roles. In this case, we can say that the non-natural role is a sub-role of an aggregate of natural roles (we may or may not want to say that it is a sub-role of each natural role in the aggregate). Thus, while monarchy may simply be a sub-role of public authority, which is a natural role, being a fire-fighter and being a president may be sub-roles of public authority and being an employee.
There may also be merely conventional roles. Merely conventional roles are of no interest to me here. They do not role-ishly result in moral duties, permissions and rights, and non-moral duties, permissions and rights are of little more interest to me than rubber ducks are to ornithologists. :-)