Subgrouping the Sogeram languages A critical appraisal of historical glottometry

Historical Glottometry is a method, recently proposed by Kalyan and François (François 2014; Kalyan & François 2018), for analyzing and representing the relationships among sister languages in a language family. We present a glottometric analysis of the Sogeram language family of Papua New Guinea and, in the process, provide an evaluation of the method. We focus on three topics that we regard as problematic: how to handle the higher incidence of cross-cutting isoglosses in the Sogeram data; how best to handle lexical innovations; and what to do when the data do not allow the analyst to be sure whether a given language underwent a given innovation or not. For each topic we compare different ways of coding and calculating the data and suggest the best way forward. We conclude by proposing changes to the way glottometric data are coded and calculated and the way glottometric results are visualized. We also discuss how to incorporate Historical Glottometry into an effective historical-linguistic research workflow.