  Ramsey drew a distinction between ‘logical’ and ‘semantical’ paradoxes, with Russell’s paradox belonging to the former category and Richard’s or Grelling’s paradoxes to the latter (1925a, [PP] 183–184). According to him, the heart of the problem was in the way the theory of types was devised to deal with the paradoxes, as understood in terms of the ‘vicious-circle principle’ (‘whatever involves all of a collection must not be one of the collection’):