Markedness distinctions can be ignored. For example, in some languages stress avoids central vowels, and falls on high peripheral vowels, yet in the Uralic language Nganasan central and high peripheral vowels are treated in the same way: stress avoids both types equally. Such ‘conflation’ of markedness categories is not only language-specific, but also phenomenon-specific. In contrast, dominance relations in markedness hierarchies are universal; e.g. stress never seeks out a central vowel when a high peripheral vowel is available. This article argues that both language-specific conflation and universal markedness relations can be expressed in Optimality Theory. Constraints that refer to a markedness hierarchy must be freely rankable and mention a contiguous range of the hierarchy, including the most marked element. The empirical focus is sonority-driven stress in Nganasan and Kiriwina. In addition, Prince & Smolensky's (1993) fixed ranking theory of markedness hierarchies is shown to be unable to produce the full range of attested conflations.