Sellars boldly proclaims that “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).  But understood in the context of his system, this is not the proclamation of a harsh, reductive scientific realism, for (1) he does not believe that describing and explaining are the only significant dimensions of human activity.  In particular, he recognizes that prescription and proscription are (a) different from description and (b) indispensable to human activity.  And (2), his conception of ontology is object-oriented; the presence of normative truths does not belie his fundamental naturalistic nominalism.  To begin to unpack these claims, we need to look at Sellars’s philosophy of language and his ontology.