 Nowadays, a more serious worry related to self-exemplification is Russell’s famous paradox, constructed as regarding the property of non-self-exemplification, which appears to exemplify itself iff it does not, thus defying the laws of logic, at least classical logic. The discovery of his paradox (and then the awareness of related puzzles) led Russell to introduce a theory of types, which institutes a total ban on self-predication by a rigid segregation of properties into a hierarchy of types (more on this in  §6.1).  The account became more complex and rigid, as Russell moved from simple to ramified type theory, which involves a distinction of orders within types (see entries on  type theory  and  Russell’s paradox,  and, for a detailed reconstruction of how Russell reacted to the paradox, Landini 1998).