Historical linguistics is the study of how languages change over time. It examines the evolution of languages, their relationships, and the processes that lead to the development of new languages. By analyzing changes in vocabulary, grammar, and pronunciation, linguists can trace the history of languages and understand how they are connected. One key aspect of historical linguistics is the reconstruction of proto-languages, which are the hypothetical common ancestors of language families. For example, Proto-Indo-European is the reconstructed ancestor of many modern languages, including English, Spanish, and Hindi. This field helps us understand cultural and social changes through language evolution.