Computational dialectology in Irish Gaelic

Computational dialectology in Irish Gaelic Brett Kessler* Department of Linguistics Stanford University Stanford CA 94305-2150 USA kessler@csli.stanford.edu Abstract Dialect groupings can be discovered ob- jectively and automatically by cluster analysis of phonetic transcriptions such as those found in a linguistic atlas. The first step in the analysis, the computa- tion of linguistic distance.between each pair of sites, can be computed as Leven- shtein distance between phonetic strings. This correlates closely with the much more laborious technique of determining and counting isoglosses, and is more ac- curate than the more familiar metric of computing Hamming distance based on whether vocabulary entries match. In the actual clustering step, traditional ag- glomerative clustering works better thaxl the top-down technique of partitioning around medoids. When agglomerative clustering of phonetic string comparison distances is applied to Gaelic, reasonable dialect boundaries are obtained, corre- sponding to national and (within Ire- land) provincial boundaries. 1 Introduction Defining dialects is one of the first tasks that lin- guists need to pursue when approaching a lan- guage. Knowing the dialect areas helps one allo- cate resources in language research and has impli- cations for language learners, publishers, broad- casters, educators, and language planners. Un- fortunately, dialect definition can be a time- consuming and ill-defined process. The traditional approach has been to plot isoglosses, delineating regions where the same word is used for the same concept, or perhaps the same pronunciation for the same phoneme. But isoglosses are frustrat- ing. The first problem, as Gaston Paris noted (apud Durand, 1889:49), is that isoglosses rarely coincide. At best, isoglosses for different features approach each other, forming vague bundles; at *I thank Martin Kay, Paul Kiparsky, Tom Wasow, and a reviewer for helpful comments. worst, isoglosses may cut across each other, de- scribing completely contradictory binary divisions of the dialect area. That is, language may vary ge- ographically in many dimensions, but the require- ments we usually impose require that a specific site be placed in a unique dialect. Traditional di- alectological methodology gives little guidance as to how to perform such reduction to one dimen- sion. A second problem is that many isoglosses do not neatly bisect the language area. Often variants do not neatly line up on two sides of a line, but are intermixed haphazardly. More importantly, for some sites information may be lacking, or the question is simply not applicable. When compar- ing how various sites pronounce the first conso- nant of a particular word, it is meaningless to ask that question if the site does not use that word. So the isogloss is incomplete and cannot be meaning- fully compared with isoglosses based on different sets of sites. The third problem is that most languages have dialect continua, such that the speech of one com- munity differs little from the speech of its neigh- bouts. Even though the cumulative effects of such differences may be great when one considers the ends of the continua (such as southern Italian ver- sus northern French), still it seems arbitrary to …

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