Ivo Hajnal dates the beginning of the diversification of Proto-Greek into the subsequent Greek dialects to a point not significantly earlier than 1700 BCE. The conventional division of the Greek dialects prior of 1955 differentiated them between a West Greek (consisting of Doric and Northwest Greek) and an East Greek (consisting of Aeolic, Arcado-Cypriot, and Attic-Ionic) group. However, after the decipherment of the Linear B script, Walter Porzig and Ernst Risch argued for a division between a Northern (consisting of Doric, Northwest Greek, and Aeolic) and a Southern (consisting of Mycenaean, Arcado-Cypriot, and Attic-Ionic) group, which remains fundamental until today.