This is the basic reasoning behind Sellars’s scientific realism.  His bold claim, “In the dimension of describing and explaining the world, science is the measure of all things, of what is that it is, and of what is not that it is not” (EPM: §41, in SPR: 173; in KMG: 253) needs proper interpretation, as mentioned above.  Sellars does not believe, for instance, that describing and explaining are the only “dimensions” of linguistic activity.  Prescribing, evaluating, and negotiating are equally indispensable dimensions of language use that go beyond the descriptive brief of science.  It is science’s job to limn the structure of empirical reality, the causal nexus within which we live, but, as his own call for a “synoptic vision” that unites a science-generated picture of empirical reality with “the language of community and individual intentions” indicates, Sellars would never hold that all our questions are to be settled by scientific investigations. 