The work presents the concept of a structural universal and the criticisms that have been leveled against it. A structural universal is a property had by an individual due to the nature of its proper parts and due to the relations obtaining between those parts. Mellor has argued that there is no reason to accept such universal in addition to the basic universals that compose them. David Lewis has argued -on the other hand- that it has not been satisfactorily explained how universals are composed by other universals. The composition by which a structural universal is given cannot be a set-theoretical construction or a mereological sum. Several proposals to explain the nature of structural universals are discussed. Finally it is argued that a...