Contents -- Part I: Background and Current Context -- Introduction to Part I -- 1. Introduction -- 2. Word Frequency in Lexical Diffusion and the Source of Morphophonological Change -- Part II: Frequency as a Determinant of Morphological Structure -- Introduction to Part II -- 3. Explanation in Morphophonemics: Changes in Provençal and Spanish Preterite Forms -- 4. On Lexical and Morphological Conditioning of Alternations: A Nonce-Probe Experiment with Spanish Verbs -- 5. Rules and Schemas in the Development and Use of the English Past Tense -- 6. Morphological Classes as Natural Categories -- 7. Are Stem Changes as Natural as Affixes? -- 8. Regular Morphology and the Lexicon -- Part III: Phonetic Change: Frequency in Context -- Introduction to Part III -- 9. The Phonology of the Lexicon: Evidence from Lexical Diffusion -- 10. Lexicalization of Sound Change and Alternating Environments -- 11. Word Frequency and Context of Use in the Lexical Diffusion of Phonetically Conditioned Sound Change -- Part IV: Frequency Effects in Mophosyntax -- Introduction to Part IV -- 12. Three Frequency Effects in Syntax -- 13. The Emergent Lexicon -- 14. The Effect of Usage on Degrees of Constituency: The Reduction of Don't in English -- 15. Sequentiality as the Basis of Constituent Structure -- 16. Mechanisms of Change in Grammaticization: The Role of Frequency -- Index -- A -- B -- C -- D -- E -- F -- G -- H -- I -- J -- K -- L -- M -- N -- O -- P -- R -- S -- T -- U -- V -- W -- Z.