This last point is crucial.  According to Sellars, rules of criticism (ought-to-be’s) have no way of being realized in the world (other than merely accidentally) except insofar as there are agents who recognize them, infer rules of action from them and thereupon undertake the requisite actions.  Unless there are agents cognizant of and acting on some rules of action, talk of any rules, including the apparently less committal rules of criticism, turns out to be empty.  We are rule-governed creatures because we conceive of ourselves as rule-governed creatures.  And, as long as we do conceive of ourselves as governed by rules and train ourselves and our progeny to recognize and live in accordance with rules, it is true that we are rule-governed creatures. By taking ourselves to be persons, agents acting for reasons in accordance with rules, we make ourselves persons. 