The work surveys comparative philology by defining the nature and aims of the science, reviewing historical theories, and arranging established facts for systematic study. It analyzes the three principal causes of linguistic change (imitation, emphasis, and laziness), explores dialectal variety, and treats speech physiology, phonology, semantics, etymology, morphology, and comparative syntax. Methodological points include the use of less-studied languages and child speech to infer earlier stages. Appendices, alphabets, diagrams, and examples are provided to clarify phonetic and structural discussions, with emphasis on preparing a clear foundation for further research rather than pursuing speculative generalization.