The Categorical Imperative, then, is connected with autonomy in a way that the Hypothetical Imperative is not. The nature of the connection can be summarized as follows. Any rational person with desires is bound by the Categorical Imperative if and only if he has an autonomous will. In fact, the Categorical Imperative is, on Kant's view, simply one way of expressing the constraints that all rational and autonomous persons would impose on themselves. One must make one's conduct conform to the Categorical Imperative, then, in order to avoid acting contrary to principles that one freely adopted. And when respect for the Categorical Imperative is the motive for one's conduct, one's actions express one's nature as an autonomous person. Thus, in a sense, the man who acts from respect for the Categorical Imperative is the most completely free.
These remarks require explanation. They may lead one to infer that a person is free only when he acts morally, but this inference would be mistaken. Kant distinguishes two different kinds of freedom. The first is what he calls "negative freedom." This is "the property (of a will) of being able to work independently of determination by alien causes." All men, good and bad, have this freedom, which consists of being able to choose to do things without one's choices being entirely the result of prior causes. In saying that men have autonomous (or positively free) wills, Kant attributes to them a second kind of freedom. This is "the property of being a law to oneself." A person is a law to himself, I take it, if he adopts principles for himself and regards himself bound by them and if he was not caused or even motivated to adopt them by any contingent circumstances (such as his desires). A person who is autonomous in this sense gives himself principles without accepting them on authority, out of fear, or even from an interest in his own or others' welfare. He regards himself bound by these principles and is disposed to follow them, but does not always do so. All men, Kant held, are autonomous in this sense. And, in fact, the only principles they adopt as autonomous persons are those expressed in the various formulations of the Categorical Imperative.
(Thomas E. Hill Jr, "The Hypothetical Imperative," The Philosophical Review 82 [October 1973]: 429-50, at 447-8 [footnotes omitted])
