This essay deals with the analysis of three concepts: principles, fundamental rights and set theory. First, the distinction between rights as simple, complex and abstract positions is analyzed. In general, rights as abstract positions (i.e., principles) are considered as – or assimilated to – fundamental rights, and only by extension this term is used to make reference to its simple or complex specifications. Normally, it is argued that fundamental rights not only are reasons for the specification of different (simple or complex) rights, but also that they cover a set of this kind of rights. Therefore, rights covered by a principle compose a set of norms, which is part of another set, that one of fundamental rights. Of course, this set is in turn included in the set of norms we usually call legal system. Within this compass, a schematic reconstruction of these rights is offered using the instruments of the set theory.