International Law in its current form is dominated by positivism and voluntarism; yet, it has accepted a number of concepts from the Natural Law tradition that seem on the face of things to ill-fit the dominant normative complex. Of primary concern here are the Natural Law notions of categorical obligation that have been brought into International Law in the form of jus cogens rules. A number of interesting questions present themselves. What are positivists doing talking about categoricals? How have they found a way to make this fit within their larger doctrine? Have positivists adopted the language of categorical obligation, but only the language, not the correlative practices? Is it simply a matter of smuggling in alien concepts and shoehorning them despite the lack of fit, or have they created something new that only seems not to fit? Ultimately, what we find is that International Law has accepted this idea in a form that ultimately is limited by voluntarism's insistence on the voluntary and specific character of all obligations.