both University of Amsterdam) and E. Hoekstra (Fryske Akademy).It contains eight chapters (an introduction, theoretical framework, five case studies and final discussion), supplemented by appendices with survey questionnaires, additional analyses of data from MAND, and summaries in English, Dutch and Frisian.In the following, I first summarise the main empirical questions and findings before then discussing the methods and theoretical framework. 1 The overall aim of the study is to empirically describe, theoretically model and explain the ongoing changes in the conjugation system of West Frisian in order to gain insight into the mechanisms of morphological change, in particular, relating to why certain changes occur and others do not (Ch. 1 Introduction, p. 1).Merkuur considers Frisian, due to its low degree of standardisation and close contact to Dutch, as a fruitful testing ground for theoretical notions of morphological variation and change.In contrast to Dutch and most other West Germanic varieties, West Frisian has retained two weak conjugation classes.This study focuses on phenomena occurring within the largest of them, weak class II, which incorporates 81% of types listed in the lexical databases of the Fryske Akademy (p.57).The class features discussed include the lack of a dental suffix in the preterite and past participle and syncretism in the category tense in the 2nd person singular.Chapter 2 then introduces the notion of morphological change adopted in the study, which essentially focuses on generalisations based on ambiguous input in acquisition, and the theoretical framework, which combines two formal approaches, Distributed Morphology and the Tolerance Principle.The subsequent chapters provide in-depth case studies.Chapters 3 and 4 address the relationship between weak class I (with infinitives in -ə, and preterites and past participles with a dental suffix) and weak class II (with infinitives in -jə, and preterites and past participles without a dental suffix) within the overall conjugation system.Merkuur investigates which classes and subclasses can be considered rule-based from a Distributed Morphology perspective (Ch.3).On this basis, she tests which of these rules are then identified as productive generalisations when the Tolerance Principle, a measure of inflectional productivity first proposed by Yang, is applied to them (Ch.4).Contributing to a long-standing discussion in the field, Merkuur then focuses on the question of whether one of the 1.I am grateful to Julie