The central note of the P.I.S. [Perfect Immutable System]. In Ptolemy's theory, Mese kata thesin, the "Mese by position," the fourth note from the bottom in all scales may have had some of the functions of a tonic in some of the modes. Mese kata dynamin, "Mese by function," the Fourth note of the Dorian Mode in the Dorian Tonos (Key ) may served a reference for relating the other modes and keys to the Dorian.
When Latin music theorists employed the Roman alphabet for musical pitch notation, they used the Greek system as their model and named mese "A".