The linguist, August Fick, hypothesized a “metamorphosis of the originally Achaean Iliad into its present Ionic form.” By Achaean he meant Aeolic Greek, and by Ionic form, Ionic Greek. He based his theory on the partial substitution of Ionic words for Aeolic ones; i.e., where the Ionic forms fit the meter, which was Dactylic hexameter, they replaced the Aeolic, but where they did not, the Aeolic was left intact. For example, Atreidēs, “sons of Atreus,” the nominative case, is Ionic, but the genitive plural is Atreidaōn, an Aeolic form, instead of the Ionic Atreideōn, which does not fit the meter.