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Semantic / Syntactic / Singular Term / Denotation / Ontology / FieldVsWright: it is not incorporated into the syntax that the singular term "4", denotes. - ((s) That means that the number is an object) - Just as in E.g. "God." - So syntax cannot be the criterion for existence.
Syntax / Field: syntactic formulations do not need the concept of the extension.
Realism, Mathematics and Modality Oxford New York 1989
Truth and the Absence of Fact Oxford New York 2001
Science without numbers Princeton New Jersey 1980