Unfortunately, such a weakening of (S3) entails a theory of evidential support which
can scarcely give comfort to the realist. After all, part of what separates the realist from the positivist is the former's belief that the evidence for a theory is evidence for
everything the theory asserts. Where the stereotypical positivist argues that the evi-dence selectively confirms only the more 'observable' parts of a theory, the realist
generally asserts (in the language of Boyd) that: