The sonority scale: categorical or gradient?

1. State of the affairs. The sonority scale has proven to be a decisive parameter to account for syntagmatic relations between segments, such as their organization within the syllable and across syllables. But, whereas there is tacit agreement about the relative sonority of some classes of segments (cf. VOWELS> GLIDES> LIQUIDS> NASALS> OBSTRUENTS, after Clements 1990), there is a pervasive controversy about the relative sonority of the specific sounds which belong to these classes. This controversy mainly concerns the pairs laterals vs. rhotics, fricatives vs. stops, voiced obstruents vs. voiceless obstruents, and also stops vs. affricates vs. fricatives, and glottals. Indeed, the relative sonority of each of these sounds varies from one study to another, basically depending on language-specific patterns. This procedure often derives on circular argumentations, since particular versions of the sonority scale are invoked to account for specific language patterns, and these specific language patterns are adduced to justify the selection of these particular versions of the sonority scale (see Ohala 1990 for discussion on this direction). Another object of traditional debate is whether it is a licit resource or not to appeal to sonority conflations and reversals to justify differences across languages. Those who disagree with this view argue that the sonority scale is universal, categorical (composed by discrete units) and impermutable, and that discrepancies across languages must exclusively be derived from constraint reranking. There are different arguments, though, which advocate a more flexible an