# Historical glottometry
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'''Historical glottometry''' is a method used in [historical linguistics](/source/historical_linguistics). It is a quantitative, [non-cladistic](/source/Cladistics) approach to [language subgrouping](/source/language_subgrouping).
The aim of historical glottometry (HG) is to address the limitations of the [tree model](/source/tree_model) when applied to [dialect continua](/source/dialect_continuum) and [linkages](/source/Linkage_(linguistics)). It acknowledges that the genealogical structure of a linkage typically consists of entangled subgroups, and provides ways to reconstruct that internal structure by measuring the relative strength of these subgroups.
This approach was developed by [Alexandre François](/source/Alexandre_Fran%C3%A7ois) ([CNRS](/source/CNRS)) and Siva Kalyan ([ANU](/source/Australian_National_University)).[François (2014).][François (2017).][Kalyan & François (2018).] While the method was initially applied to [Oceanic languages](/source/Oceanic_languages), in recent years it has been applied to a much broader range of language families.
==Rationale==
Historical Glottometry grew out of the observation that a large number of [language families](/source/language_families) in the world form [linkages](/source/Linkage_(linguistics)) (a term coined by [Malcolm Ross](/source/Malcolm_Ross_(linguist))), i.e. they evolved out of former [dialect continua](/source/Dialect_continuum) in which historical innovations tend to overlap. Such linkages do not conform with the [Tree model](/source/Tree_model) often used in historical linguistics, which presupposes that innovations should be nested. This common situation is better approached using the [Wave model](/source/Wave_model).[Source: [https://hg.hypotheses.org/tutorial A tutorial on Historical Glottometry], by Kalyan & François.]
# each [subgroup](/source/Clade) is defined by ''exclusively shared innovations'' (a principle first expressed by [Leskien](/source/August_Leskien) [1876]), i.e. linguistic [synapomorphies](/source/Synapomorphy_and_apomorphy);
# subgroups are allowed to [intersect](/source/Intersection_(set_theory)) (as expected under the [Wave model](/source/Wave_model));
# the “strength” of each subgroup is measured on a continuous scale (rather than subgroups simply being absent or present). That strength is assessed using two ratings, named ''cohesiveness'' and ''subgroupiness''.[{{Cite journal |last1=Jacques |first1=Guillaume |author-link1=Guillaume Jacques |last2=List |first2=Johann-Mattis |author-link2=Johann-Mattis List |date= 2019 |title= Why we need tree models in linguistic reconstruction (and when we should apply them) |journal=Journal of Historical Linguistics |volume=9 |issue=1 |pages=128–167 |doi=10.1075/jhl.17008.mat |hdl=21.11116/0000-0004-4D2E-4 |s2cid=52220491 |issn= 1875-6719|hdl-access=free }}] show that the concept of ''[incomplete lineage sorting](/source/incomplete_lineage_sorting)'' can be applied to account for non-treelike phenomena in language evolution. Kalyan and [François](/source/Alexandre_Fran%C3%A7ois) (2019) concur that "Historical Glottometry does not challenge the family tree model once ''incomplete lineage sorting'' has been taken into account"[Kalyan & François (2019).]{{rp|174}} – provided the internal variation discussed in the analysis includes the [geographical (dialectal)](/source/Variation_(linguistics)) dimension.