This work develops a parallelist theory of word formation based on the notion of paradigmatic identity. Words related by morphology may be phonologically similar, beyond what is expected on the basis of their shared constituents, and achieving this similarity can lead to phonotactic violations. Following an elaboration of the theoretical framework, case studies are presented to show how paradigmatic faithfulness can supercede phonotactics and force related words to be identical in featural content or prosodic organization.