Bybee's relevance hierarchy

Bybee 1985 ranks the verbal inflectional categories by their relevance to the verb, the extent to which the category's meaning directly affects the meaning of the stem: valence, voice, aspect, tense, mood and agreement "are ranked for relevance to verbs in that order". A more relevant category is predicted to have morphological expression, inflectional or derivational, in more languages, to sit closer to the stem, and to fuse with it more tightly. The scale alone does not predict which categories are most often inflectional: generality works against the most relevant, so inflection is likeliest in the middle of the scale.

RelevanceHierarchy is a comparative concept, not a universal slot inventory: languages own the slot types of their AffixTemplates (Mayan.VerbSlot, Japanese.Verb.Slot), and a relevance claim pulls the order back along a partial map from slots to categories supplied by the study that draws the comparison. A slot sequence read stem-outward respects the hierarchy when it is List.SortedLE.

Main definitions

• Morphology.RelevanceHierarchy: Bybee's six categories, linearly ordered from the most relevant.

Implementation notes

Bybee calls the order approximate, and her diagram of it lists number, person and gender agreement as three rows at the bottom; the hierarchy takes her single category of agreement, which is what her morpheme-order survey and later comparisons test. Categories outside her list, such as derivation, negation or nonfiniteness, have no rank: a slot of that kind maps to nothing.

References

• J. Bybee, Morphology: A Study of the Relation between Meaning and Form (1985)