Rule composition makes it possible to model an important kind of deviation from the rule independence criterion – cases in which the application of one rule is directly dependent on that of another, carrier rule. In such cases, the only use of the dependent rule is as part of a composite rule incorporating both the dependent and its carrier. Where the definition of a word form involves two carrier rules, it can further happen that the same dependent rule composes with both of them, engendering a pattern of multiple exponence that deviates from the unique sequence criterion. I discuss two cases of this sort of rule dependency: Limbu verb morphology exhibits a pattern in which dependent rules compose with their carrier rules; Sanskrit presents a pattern of the reverse sort, in which a carrier rule composes with its dependent.

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.

In this chapter, I discuss the preliminary assumptions of the rule-combining approach to morphotactics and advance the two fundamental hypotheses that underlie it: the morphotactic holism hypothesis and the morphotactic variety hypothesis (Section 1.2). In Section 1.3, I review previous proposals that provide empirical support for the morphotactic holism hypothesis, which (unlike the morphotactic variety hypothesis) is not a novel idea. In Section 1.4, I discuss the nature of canonical morphotactics, for which I introduce ten criterial characteristics, construed in rule-based terms. In Section 1.5, I give examples of phenomena that possess these characteristics as well as of phenomena that do not apparently possess them. The morphotactic phenomena to be analyzed in the following chapters deviate from some of these canonical characteristics, but reinforce conformity to others provided that a rule-combining approach is assumed. In Section 1.6, I anticipate the range of topics to be discussed in subsequent chapters.