1) In 1786, Sir William Jones suggested that languages from different geographical areas had a common ancestor, launching the field of linguistic investigation into language history and change.
2) The Proto-Indo-European language is reconstructed as the common ancestor of Indo-European languages based on comparative methods analyzing cognates across languages.
3) English history is usually divided into Old English, Middle English, and Modern English periods, with each experiencing changes in sounds, syntax, borrowing, and meanings due to various influences over time.