As is well known, David Easton defines the political system as emerging from those social interactions undertaken in relation to the authoritative allocation of values for a society. This paper explains two normative services that Easton’s definition can provide for political science; one is explanatory, the other evaluative. The explanatory service is to show both the distinctiveness of political science as a social science and to serve as a standard, or norm, by which to set the boundaries of the profession’s subject matter. Secondly, Easton’s theory of the political system as an input/output model can serve as a standard by which to assess the “goodness” of a political system, and for comparing the goodness of systems. Assessing such goodness is not a matter of moral approval or approbation, but more like the taxonomist assessing the goodness of a specimen, as to both its categorical fit and its health.