Proto-languages are hypothetical, reconstructed languages that are believed to be the common ancestors of a group of related languages. Linguists use comparative methods to identify similarities and differences among languages, allowing them to infer the features of these ancient languages. For example, the Proto-Indo-European language is the reconstructed ancestor of many modern languages, including English, Spanish, and Hindi. These proto-languages are not directly attested in written form; instead, they are inferred from the study of existing languages. By analyzing vocabulary, grammar, and phonetics, researchers can piece together aspects of these early languages, providing insights into the cultures and societies that spoke them.