 To understand that account, one needs first to appreciate the difference between the syntactic view of scientific theories and van Fraassen’s preferred semantic view of scientific theories. On the syntactic view, a theory is given by an enumeration of theorems, expressed in some one particular language. In contrast, on the semantic view, a theory is given by the specification of a class of structures (describable in various languages) that are the theory’s models (the determinate structures of which the theory holds true). As van Fraassen says,