How do linguists reconstruct Proto-Indo-European without written records of it?

Linguists reconstruct Proto-Indo-European (PIE)—a hypothetical ancestor language with no surviving written records—primarily through the comparative method.

This process involves systematically comparing related words and grammatical structures across descendant languages, such as Sanskrit, Greek, Latin, and Germanic languages. By identifying regular sound correspondences—such as Grimm’s Law—linguists can derive ancestral forms, which are marked in literature with an asterisk (e.g., the reconstructed word for "ten," *dekm).12

Reconstruction is further supported by:
* Internal reconstruction: Analyzing irregular patterns within a single language to infer earlier, regular states.3
* Hypothesis and validation: Scholars like Ferdinand de Saussure proposed structural rules for PIE that were later confirmed by the discovery of the Hittite language.1
* Interdisciplinary evidence: Linguistic findings are often correlated with archaeological data, such as the Kurgan culture, to provide historical context for the language's expansion.4