Add to ORKGIn nineteenth century linguistics the interest in common features of language, universally shared among the different historical languages, shows both in the quest for the proto-language and in the identification of the linguistic 'type' to which the different languages individually belong. The first case corresponds to historical-comparative linguistics, which, at least initially, advocated linguistic monogenesis. The second research perspective opens a most fruitful line of enquiry in the history of linguistic thought which, looking for individuation of further possible similarity relationships, elaborates the hypothesis of affinity through contact. This model is at the origin of interesting reflections developed in the 19th and 20th cent...