Phonology is a very diverse field of study. Van Oostendorp et al.'s (Reference van Oostendorp, Ewen, Hume and Rice2011) 124-chapter (3,192 pages), 5-volume companion to phonology stands out as an excellent testament to that fact. Thus, the task of organizing a handbook that expressly adds the dimension of time to phonological theory is a patently difficult enterprise. Honeybone and Salmons approach that task by dispensing with linear one-to-one trajectories from methods to data to theories. Instead, the editors have adopted a network-like organization of the chapters and parts that enables them to showcase the richness of the field within a 37-chapter (666 pages) volume. The network-like organization effectively highlights the numerous differences across the field without needing to reconcile them. The chapters are followed by a comprehensive list of references (92 pages) and helpful indices for languages, author names, and subjects (34 pages).

Part I begins with Honeybone & Salmons's introduction (chapter 1), which briefly discusses the volume's structure, and then lays out six questions that are central to research on phonological change. They expressly request that readers “look for more abstract structure” (p. 3) in the book by considering the interconnectedness of chapters beyond the current organization. To this end, I discuss the chapters within each section out of sequence. However, I refrain from altogether regrouping chapters from different parts so that this review stays reasonably true to the book's structure.

The remaining chapters of part I function as a literature review for the field. As such, they are occupied with the earliest pursuits in historical phonology and the research questions that stem from those efforts. Murray (chapter 2) traces the earliest notions of sound change through to the neogrammarian program at the end of the 19th century; the emergence of structuralism in the 20th century is taken up by Salmons & Honeybone (chapter 3). Neogrammarian and structuralist research questions at least partly underlie every subsequent chapter of the handbook. Thus, chapters 2 and 3 allow the reader to see how those early inquiries relate to issues in contemporary phonological theory.

Part II is entitled “Evidence and Methods in Historical Phonology”. Chapters 5–7 focus on evidence from written data. Unger (chapter 6) presents orthographic evidence in the Sino-Xenic sphere, while Minkova (chapter 5) and Lass (chapter 7) offer case studies in Old and Middle English, respectively. Two chapters on historical orthography in English may seem excessive at first glance, but this is far from the case. The two chapters present an excellent range of data that address both the reliability and the difficulty of reconstructing a phonological system on the basis of poetic and orthographic practice. Evidence from spoken data is discussed by Maguire (chapter 11) and Gordon (chapter 12). The former considers the use of recorded speech for historical phonology; the latter applies sociolinguistic methodology to spoken data to gain insight into sound changes such as chain shifts, mergers, and near-mergers.

The remaining chapters of part II concern reconstructed data. Fox (chapter 4) reviews internal and external reconstruction. Kümmel (chapter 8) considers the use of typological generalizations for reconstructive purposes, and a modern computational approach to reconstruction is taken up by Kessler (chapter 9). Wedel (chapter 10) deliberates on the use of simulation to evaluate models of change and to generate new hypotheses regarding the way that changes might unfold. All in all, these chapters provide a crisp overview of reconstruction and give the reader a good idea of what the state of the art looks like.

The title of part III is “Types of Phonological Change”. As the title suggests, these chapters speak to explicanda in historical phonology. The section addresses changes that are segmental (Cser, section 13.3.1), tonal (Ratliff, chapter 16), prosodic (Cser, section 13.3.2; Lahiri, chapter 15; Smith & Ussishkin, chapter 17), and morphophonological (Fertig, chapter 14). Thus, part III covers considerable empirical ground. Taken on its own, this part may seem a bit exiguous to readers. To some extent, this is because a number of topics that one would especially like to read about in this part are simply taken up elsewhere in the book. Chain shifts, for example, are palpably missing from the part III docket, but receive considerable attention in other parts (see section 3.3.3, chapter 12, section 18.2.3, 25.5.1, etc.). Generally speaking, any incompleteness in part III is due to the volume's network-like organization. For instance, splits and mergers fall under the chapter on tone here, but are discussed in the context of segmental phonology in other chapters. That lack of alignment between chapters will be beneficial to more experienced researchers, who can connect tones and segments. However, it stands out as a potential obstacle when the book is used for more rudimentary instruction.

Most books on historical linguistics tend to focus on Indo-European, and often more narrowly Germanic, languages, while other language families receive significantly less attention. That is largely an unavoidable consequence of the way the field has developed. Part III makes a concerted effort to fill that gap. Readers will especially appreciate Ratliff's contribution on tonal developments and the comparison of Germanic prosodic templates with Mixtec in Smith & Ussishkin's chapter. Yet the survey of processes in this part still tips in favor of Indo-European, and especially Germanic, languages. Thus, there is a bit of a lost opportunity to present historically familiar developments from languages with less familiar histories. An additional chapter on phonetic-level changes would have strengthened this part's connected-ness to the rest of the book. The chapter could showcase neutralizations that are phonologically complete but phonetically partial (for example, Port & O'Dell Reference Port and O’Dell1985); or it could present research in sociophonetic variation (for example, Foulkes & Hay Reference Foulkes, Hay, MacWhinney and O’Grady2015).

I mention part V prior to part IV, since these chapters on theoretical historical phonology are, essentially, the explicantia chapters. However, it must be emphasized here that many chapters outside of this part also include explanations and analyses of sound change. Part V includes overviews of three functional (phonetic and/or frequency sensitive) models of change, namely, natural phonology (Donegan & Nathan, chapter 25), articulatory phonology (Bybee, chapter 27) and evolutionary phonology (Blevins, chapter 28). The remaining chapters attend to models of change that fall out from abstract structures, namely, features (Purnell & Raimy, chapter 30), phonemes (Kiparsky, chapter 32), rules (Dresher, chapter 29), constraints (Holt, chapter 31, Kiparsky, chapter 32), and prosodic constituents (Mailhammer et al., chapter 26). A nice aspect of part V is the sense of harmony between functional and theoretical modes of analysis. That harmony is facilitated by helpful discussions of the problems and limitations endemic to one theory that leave space open for the next. Cross-references in this part are especially beneficial.

Owing to the network-like structure of the book, the explicanda from part III do not correspond directly to the explicantia in part V. However, what comes at the cost of neat one-to-one trajectories is a volume that is both thorough with respect to the kinds of data discussed and representative with respect to theory. Since the number of theoretical frameworks is easily as abundant as the number of processes to be investigated, the book's structure is both practical and successful. The drawback, of course, is that a reader unfamiliar with any given framework will unavoidably be left wondering how that framework captures certain types of data.

Part IV highlights controversies in historical phonology. Chapters 19 and 22 relate to the restrictiveness of sound change. Scheer (chapter 19) expounds on “crazy rules” and the extent to which these seemingly unnatural patterns reflect true sound changes or coincidental patterns. Bermúdez-Otero (chapter 22) argues for a life cycle of sound changes that delimits the way those changes advance through grammar at stem, word, and phrase levels. Chapters 18 and 20 look at sources of change. Foulkes & Vihman (chapter 18) consider language transmission and the extent to which correct and incorrect forms in first language acquisition mirror changes from earlier to later forms within a linguistic community. Hale at al. (chapter 20) offer a more theoretical view of sound change that stems from underlying structure (I-Language). Finally, chapters 21 and 23 consider cases of apparent exceptionality. Phillips (chapter 21) shows how much systematicity is involved with lexical diffusion; Jones (chapter 23) finds systematicity at the level of the individual.

At first blush, part IV may not seem to introduce controversies in phonological change so much as it offers perspectives on diachronic phonology that are controversial. I say that because many chapters in this section take specific positions and do not give equal treatment to opposing views, as might give readers a true sense of controversy. At the same time, one can and should read more than 200 years of debate into part IV insofar as the chapters reflect contemporary research that is still deliberating on questions first asked by the neogrammarians.

Part IV would have benefited from some discussion of the way that controversies in phonological theory bear on the analysis of historical sound change. A case in point is the analysis of Old English Breaking. This prosodically and segmentally conditioned development involves a vocalization according to Howell Reference Howell1991, an assimilation of backness following Lass & Anderson Reference Lass and Anderson1975, and a dissimilation of frontness in Kostakis's (Reference Kostakis2015) view. These differing perspectives emerge not only because featural models and representations of sonority have never been unified within a mainstream phonological framework, but also because changes may appear to be assimilatory or dissimilatory depending on the features that one holds as active.

The sixth and final part is about exogenous factors. This part is largely concerned with the plasticity (grammatical alterability) of different age groups within a linguistic community and the importance of that plasticity for propagating phonological developments. Post-adolescent plasticity is observed in real time sociolinguistic studies, as discussed by Bowie & Yaeger-Dror (chapter 34). Additionally, Eckman & Iverson (chapter 36) identify patterns of L2 acquisition that effect change on L1 phonology. Adult plasticity also relates to Uffmann's (chapter 37) chapter on the implications that adaptation and non-adaptation of loan words have for phonological grammars. In D’Arcy's contribution (chapter 33), prepubescent plasticity is the main force driving change in progress. Schreier (chapter 35) also mentions the crucial role of children in koinéization. However, the chapter focuses primarily on the typology of compromise forms that develop from competing dialectal structures.

The handbook will be an enduring resource for scholars in the field. It exposes readers to new analytical frameworks and methodologies, and also provides significant updates to age-old techniques such as the comparative method. The book relates the research questions of multiple conceptions of phonology—from functional to theoretical—to an array of diachronic processes. While scholars of Germanic linguistics will be familiar with many of the changes discussed, they will appreciate the fresh insights into those phenomena. They can also look forward to a fair measure of historical phonology beyond the scope of Germanic and Indo-European. All of this is accomplished in a single volume by implementing a network-like organization between data, methods, and analyses. Although readers will undoubtedly find some gaps in the book, those gaps are few and outweighed by an unmistakable comprehensive- ness. Readers will be pleased with the book's vision of historical phonology and its cues on the direction of the field.