How do linguists use sound correspondences to show that Sino-Tibetan languages are related?

Linguists demonstrate that Sino-Tibetan languages are related primarily by identifying systematic phonological correspondences within shared vocabulary. This approach relies on the comparative method, a cornerstone of historical linguistics that assumes languages sharing a common ancestor will exhibit regular, predictable sound changes across their respective lexicons.12

By comparing basic vocabulary items—such as words for "eye," "sun," or "kill"—across different languages like Old Chinese and Old Tibetan, linguists can identify sound resemblances that are too consistent to be coincidental. These correspondences allow researchers to reconstruct ancestral forms, often marked with an asterisk, from which modern language features are derived.32

In the study of these languages, experts prioritize perfect phonetic correspondences over perfect semantic equivalences, as the latter can sometimes be misleading. Furthermore, linguists account for the evolution of sound systems by analyzing how factors like prefixes, voicing, and aspiration interact over time to produce the diverse phonological patterns observed in modern daughter languages.34