Linked from
The 27 pages that link to Proto-language, each with the reason it gives.
Language familyBroader topic: Each family is defined by descent from a common proto-language.
LanguageRelated: It offers a method for tracing language families into the past.
CognateNarrower topic: Cognates are traced back to a shared ancestral form in a proto-language.
Grimm's lawRelated: Proto-Indo-European consonants are inferred rather than directly attested.