Contemporary American medical ethics was born during a period of social ferment, a key theme of which was the espousal of individual rights. Driven by complex cultural forces united in the effort to protect individuality and self-determined choices, an extrapolation from case law to rights of patients was accomplished under the philosophical auspices of 'autonomy.' Autonomy has a complex history; arising in the modern period as the idea of self-governance, it received its most ambitious philosophical elaboration in Kant's moral philosophy. In examining the Kantian construction, it is evident that neither his universal moral imperative nor his rigorous application of self-legislated ethical action can sustain our own notions of moral agency in a pragmatic, pluralistic society. But the Kantian position is useful in highlighting that self-governance is not equivalent to 'autonomy,' and this distinction defines the limits of autonomy in the clinical setting. A critique of Engelhardt's idea of 'principle of permission' is used to illustrate autonomy's eclipse as a governing principle for medical ethics.