thus, all sibilant obstruents (fricatives and affricates) in these languages are divided into two groups, +anterior (, , ) and -anterior (, , ). in navajo, as in most languages with consonant harmony, there is a constraint on the shape of roots (a well-formedness constraint) that is identical to the harmony process. all roots with sibiliant affricates or fricatives have the same value for anteriority. shaw (1991) provides a phonological analysis of this process, using data from research on tahltan.