 Carnap held that claims about the “real” existence of entities (concrete or abstract) do not have cognitive content. They are pseudo-statements. However, he admitted: (a) that there are sentences in science that use terms that designate mathematical entities (such as numbers); and (b) that semantic analysis seems to require entities like properties and propositions. Since mathematical entities, properties, and propositions are traditionally considered abstract, he wanted to clarify how it is possible to accept a language referring to abstract entities without adopting what he considered pseudo-sentences about such entities’ objective reality. Carnap’s famous paper (1950 [1956]) contained an attempt to show that, without embracing Platonism, one can use a language referring to abstract entities.