My fellow students at UCLA all helped create an atmosphere of creativity and discovery, for which I am grateful. But in particular, I wish to thank Edward Flemming, one of the most brilliant people I've ever met, without whose pioneering work this dissertation would be inconceivable; Richard Wright, whose brain I have shamelessly and repeatedly picked (I hope I can somehow eventually repay the debt); Rod Casali, for helping me pretend to know something about physics; and Peggy (sorry, Margaret)MacEachern, for general camaraderie, thought-provoking discussions on a variety of linguistic and philosophical issues, and drawings of horses for Miriam.Thanks to Amy Weinberg, my first phonology teacher(!), who helped rescue me from a legal career (shudder), and to Marie Huffman, who got me excited about phonology and very wisely told me to go to UCLA.To Donna Albino: thanks for helping me stay centered as a human being.To my wife Suzanne: I started graduate school as an anti-sexist egalitarian idealist, and as this dissertation took over my life, I gradually degenerated into a typical nerd husband who spent all day hunched over the computer while you cooked, cleaned, and took care of the girls, as well as taught. Thank you. And now it's your turn.To my daughters, Miriam and Naomi: OK, I'm ready to play with you now. Professor Donca Steriade, ChairDespite the pervasiveness of lenition in the sound systems of natural language, this class of patterns has eluded adequate characterization in previous theories of phonology. Specifically, previous theories have failed to capture formally the phonetic unity of the various lenition processes (e.g. degemination, voicing, spirantization, debuccalization, deletion), or to account for the environments in which lenition typically occurs.