Tham khảo Ngữ_hệ_Ấn-Âu

  1. ↑ Nordhoff, Sebastian; Hammarström, Harald; Forkel, Robert và đồng nghiệp biên tập (2013). “Indo-European”. Glottolog. Leipzig: Max Planck Institute for Evolutionary Anthropology.  Gợi ý |số biên tập viên= (trợ giúp)
  2. ↑ “Ethnologue report for Indo-European”. Ethnologue.com. 
  3. 1 2 3 Auroux, Sylvain (2000). History of the Language Sciences. Berlin, New York: Walter de Gruyter. tr. 1156. ISBN 3-11-016735-2. 
  4. ↑ Robinson, Andrew (2007). The Last Man Who Knew Everything: Thomas Young, the Anonymous Genius who Proved Newton Wrong and Deciphered the Rosetta Stone, among Other Surprising Feats. Penguin. ISBN 0-13-134304-1. 
  5. ↑ In London Quarterly Review X/2 1813.; cf. Szemerényi 1999:12, footnote 6