Historical linguistics compares vocabulary and grammatical structure systematically across languages to establish genuine genetic relationship and reconstruct a shared ancestor language, rather than relying on superficial resemblance between words that can arise by coincidence or borrowing. The British judge and philologist William Jones set the discipline in motion in a 1786 address to the Asiatic Society of Bengal, arguing from systematic grammatical comparison that Sanskrit, Greek and Latin shared a common source no longer extant, a claim that could not be dismissed as coincidence given the depth and structure of the resemblance, and that launched the comparative method later linguists formalized into a rigorous discipline.
A scripture's or a liturgical tradition's own language carries a documented genetic history, and historical linguistics is what establishes which family a language actually belongs to and what that placement can and cannot say about a text's age or origin, independent of a tradition's own account of its scripture's language as unique or divinely given. The atlas relies on the discipline wherever a claim rests on a scripture's language being related, or unrelated, to another tradition's.