Eventually, the texts of literary Attic were widely studied far beyond their homeland: first in the classical civilizations of the Mediterranean, including in Ancient Rome and the larger Hellenistic world, and later in the Muslim world, Europe, and other parts of the world touched by those civilizations.
By the late 5th century, the concurrent use of elements of the Ionic system with the traditional local alphabet had become common in private writing, and in 403 BC, it was decreed that public writing would switch to the new Ionic orthography, as part of the reform following the Thirty Tyrants.
The plural is the same in both cases, gnomai and theai, but other sound changes were more important in its formation.
For example, original -as in the nominative plural was replaced by the diphthong -ai, which did not change from a to e.
Later Greek literature wrote about three main dialects: Aeolic, Doric, and Ionic; Attic was part of the Ionic dialect group.
"Old Attic" is used in reference to the dialect of Thucydides (460-400 BC) and the dramatists of 5th-century Athens whereas "New Attic" is used for the language of later writers following conventionally the accession in 285 BC of Greek-speaking Ptolemy II to the throne of Egypt.