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A central question within morphological theory is whether an adequate description of inflection necessitates connections between and among inflectionally related forms, i.e. paradigmatic structure. Researchers have recently used periphrasis and paradigmatic gaps to demonstrate the descriptive capabilities of paradigms, but in doing so have expanded the domain of inflectional structure into the traditional realm of syntax. This expanded structure is justified only if an adequate description of gaps not only allows for but also requires reference to paradigmatic structure. In this dissertation I argue that crucial evidence that paradigmatic structure underpins gaps is to be found in speakers ’ reactions to inflectional defectiveness. I show through a series of experiments and distributional statistics that gaps in the genitive plural of Modern Greek nouns and the first person singular non-past of Russian verbs arose from speakers ’ insecurity over competition between paradigmatic patterns of inflection. The appearance of the gaps can thus be adequately explained only with reference to the inflectional paradigm. I formalize this approach using a Word and Paradigm mode