Historical reconstruction of languages relies on the comparative method, which itself depends on the notion of the regularity of change. The regularity of sound change is the famous Neogrammarian Hypothesis: "sound change takes place according to laws that admit no exception." The comparative method, however, is not restricted to the consideration of sound change, and neither is the assumption of regularity. Syntactic, morphological, and semantic change are all amenable in varying degrees, to comparative reconstruction, and each type of change is constrained in ways that enable the researcher to distinguish between regular and more irregular changes. This volume draws together studies by scholars engaged in historical reconstruction, all focussing on the subject of regularity and irregularity in the comparative method. A wide range of languages are represented, including Chinese, Germanic, and Austronesian.
Durie and Ross gather essays ostensibly examining the extent to which the Neogrammarian hypothesis that sound change is regular holds up. Large portions of this book are fairly characterised as unhelpful shit-stirring, with straw-manning, excessive pedantry, and plain ahistoricism being the rule rather than the exception for most of the papers (not all of them: Lyle Campbell's contribution is, as you might expect, a cut above the rest—unsurprisingly, he disagrees with the point the editors are trying to make—and George Grace's is at least thoughtful and careful). To some extent the core of the "controversy" here is just a meaningless quibble over whether you view some of the more sophisticated methods used to explain certain sound changes (including things as basic as analogy and morphological conditioning) as refuting the Neogrammarian hypothesis or not—obviously nobody really does and it's not a particularly meaningful discussion anyway, but you can certainly get a book published on the back of it, and the main conclusion to draw here is that a lot of people in the woollier areas of linguistics (sociolinguistics, psycholinguistics) and/or Australia slept through their undergrad classes.
(Campbell and Ross inadvertently provide an excellent demonstration of academics who view jargon as a tool to aid communication on the one hand and academics who view it as a way to gate-keep, obscure lack of substance, and self-aggrandise on the other: Campbell's essay is full of language that can appear daunting at first glance to the untrained outsider but is actually precise, conventional, and no more complicated than it needs to be, whereas Ross pointlessly coins new terminology ("metatypy"), uses immensely pretentious words for no reason other than that they look clever ("esoterogeny", "exoterogeny"), and generally reads like a parody of bad, impenetrable academic writing. Every field has its Rosses to a degree, but you can typically use the proportion of Rosses to Campbells to judge how healthy and legitimate it is. Linguistics as a whole is in good shape, I think, but some of its subfields are very much not. Actually, another useful heuristic for that is the amount of bad math that gets marshalled to provide apparent legitimacy to desirable conclusions (mathwashing), for which Johanna Nichols' paper, whose calculations of phoneme probabilities a high-schooler could skewer, can serve as an archetype. Two cautionary tales for the price of one: an unexpectedly helpful book after all.)
While historical-comparative linguistics had traditionally been driven by the Neogrammarian ideal that sound change is regular and exceptionless, and one just has to formulate the right rules, advances in the 20th century slightly altered that picture. The sociolinguistics work of Labov, for instance, proved that sound changes could spread gradually through the lexicon, and this process might be interrupted before completion. Dialect-mixing too is better understood today. With that in mind, several linguistics contributed to this mid-1990s volume The Comparative Method Reviewed that tests the comparative method and proposes refinements.
Johanna Nichols presents how the comparative method, as traditionally employed, contains a heuristic component. Few historical linguistics have a rigorous background in statistics, and it is enlightening to read her explanation of how a firm cognate set (her example are the Indo-European “widow” words) would be extremely unlikely to arise by chance.
Lyle Campbell affirms the general value of the comparative method, but notes irregular sound changes that should be taken into account. He gives real-world examples of sound symbolism and homophone avoidance. John Newman's paper uses the history of Cantonese as an example of irregular sound change through taboo avoidance or influence from the literary register. Mark Durie advocates the use of variable rule analysis, treating sound laws as probabilistic, not categorical. His data for the paper is drawn from a computer database of early Germanic forms.
Several papers, by Grace, Blust, and Ross, use Austronesian languages examples. This family is well-reconstructed, but nonetheles features what Blust calls “pandemic irregularity”. These authors explore how Sprachbund phenomenon can be just as much a force for sound change as “language-internal” processes.
Harold Koch's paper shed further light on how morphology can affect phonological change, and is important reading for anyone who has finished a basic textbook of historical linguistics. Finally, in what might be the most ambitious paper in the book, David Wilkins traces the web of semantic shifts that can happen to roots and complicate the issue of finding cognates.
Almost two decades after its publication, this collection remains very valuable. Interested readers might want to also look at Ringe & Eska’s Historical Linguistics: Towards a 21st-Century Reintegration, which reflects more recent research and deals with the effects of second-language acquisition, but this volume too helps bring people up to speed with newish trends in linguistics.