I discuss different kinds of deviation from the parallel sequence criterion; I illustrate with detailed examples from Fula, Udmurt, and Eastern Mari. In Fula verb inflection, rules of subject and object marking involve a default applicational sequence that is overridden in specific circumstances by the opposite sequence of application; this deviation can by modeled by postulating two patterns of rule composition, one realizing the default sequence and the other overriding that default. Udmurt noun inflection is different, since it involves two patterns of rule composition that do not stand in a default/override relation but are instead simply complementary. Nevertheless, the Fula evidence and the Udmurt evidence both conform to the unique sequence criterion. The declensional morphology of Eastern Mari, by contrast, deviates from that criterion, since it allows alternative acceptable sequences of rule application; in the rule-combining approach to morphotactics, these can be seen as involving alternative patterns of rule composition realizing the same morphosyntactic content.

Situating the rule-combining approach to morphotactics in a wider theoretical context, I summarize its implications for the architecture of Paradigm Function Morphology and for schema unification in Construction Morphology. I further contrast the exponence-driven conception of morphotactics embodied by the rule-combining approach with the very different word-skeletal approach to morphotactics, drawing attention to two advantages of the rule-combining approach. First, it affords a more parsimonious inventory of morphological operations than is assumed in Distributed Morphology. Second, it avoids the cumbersome theoretical commitments of Information-based Morphology (the assumptions of position-based ordering, rule anchoring, and distributional pigeonholing), which entail numerous complications in the analysis of a language’s morphotactics. The distinct assumptions on which the rule-combining approach rests (those of combination-based ordering, unanchored rules, and distributional multidetermination) afford morphotactic analyses that are at once simpler and more explanatory.