The empirical–normative distinction is taken by many political scientists to be exclusive and fundamental. Yet if the distinction is deep and exclusive then any theory, or any of its components, must be either empirical or normative but not simultaneously both. If this is the case then each theoretical statement will have as its central verb either an ‘is’ or an ‘ought’ (or some equivalent) and no statement taking an ‘ought’ as its central verb will be derivable from any statement taking an ‘is’ as its central verb. Correlatively no purely descriptive statement or conjunction of such statements will warrant any normative or evaluative conclusion.