What, exactly, is it about jus cogens that distinguishes it from ordinary international law? In answering this question, international lawyers usually resort to the “the Legal-Consequences-as-Criterion Theory”: while ordinary international law can be rebutted or modified in accordance with the duly expressed will of states, jus cogens norms permit no derogation and allow modification only by the creation of a new norm having the same character. In the present essay, this theory is subjected to analysis and assessment. Section 2 inquires into the relationship between the Legal-Consequences-as-Criterion Theory and the general definition of jus cogens reflected in Article 53 of the 1969 Vienna Convention. As argued, Article 53 is entirely reliant upon the validity of the Legal-Consequences-as-Criterion Theory. Sections 3 and 4 inquire into the assumptions underlying this same Theory. As argued, the Theory does not provide good reasons for the distinction between jus cogens and ordinary international law.