The Indo-European language family comprises a vast number of languages and dialects spoken throughout the world today. All of these languages are descended from a common ancestor known as Proto-Indo-European, which scholars estimate was spoken about six thousand years ago. This common ancestor has been reconstructed by historical linguists using the comparative method. Although there is disagreement about the historical relationship of these languages to each other, this glossary uses the neo-traditional model of Indo-European phylogeny which states that the main branches of the family are Albanian, Anatolian, Armenian, Balto-Slavic, Celtic, Germanic, Hellenic, Indo-Iranian, Italic, and Tocharian.