Dorian mode

Dorian mode or Doric mode can refer to three very different but interrelated subjects: one of the Ancient Greek harmoniai (characteristic melodic behaviour, or the scale structure associated with it), one of the medieval musical modes, or, most commonly, one of the modern modal diatonic scales, corresponding to the white notes from D to D, or any transposition of this, for example the scale from C to C with both E and B flattened.

The Dorian mode (properly harmonia or tonos) is named after the Dorian Greeks. Applied to a whole octave, the Dorian octave species was built upon two tetrachords (four-note segments) separated by a whole tone, running from the hypate meson to the nete diezeugmenon. In the enharmonic genus, the intervals in each tetrachord are quarter-tone–quarter-tone–major third; in the chromatic genus, semitone-semitone-minor third; in the diatonic genus, semitone-tone-tone. In the diatonic genus, the sequence over the octave is the same as that produced by playing all the white notes of a piano ascending from E to E: E F G A | B C D E, a sequence equivalent to the modern Phrygian mode. Placing the single tone at the bottom of the scale followed by two conjunct tetrachords (that is, the top note of the first tetrachord is also the bottom note of the second), produces the Hypodorian ("below Dorian") octave species: A | B C D E | (E) F G A. Placing the two tetrachords together and the single tone at the top of the scale produces the Mixolydian octave species, a note sequence equivalent to modern Locrian mode.

The early Byzantine church developed a system of eight musical modes (the octoechoi), which served as a model for medieval European chant theorists when they developed their own modal classification system starting in the 9th century. The success of the Western synthesis of this system with elements from the fourth book of De institutione musica of Boethius, created the false impression that the Byzantine oktōēchos were inherited directly from ancient Greece. Originally used to designate one of the traditional harmoniai of Greek theory (a term with various meanings, including the sense of an octave consisting of eight tones), the name was appropriated (along with six others) by the 2nd-century theorist Ptolemy to designate his seven tonoi, or transposition keys. Four centuries later, Boethius interpreted Ptolemy in Latin, still with the meaning of transposition keys, not scales. When chant theory was first being formulated in the 9th century, these seven names plus an eighth, Hypermixolydian (later changed to Hypomixolydian), were again re-appropriated in the anonymous treatise Alia Musica. A commentary on that treatise, called the Nova expositio, first gave it a new sense as one of a set of eight diatonic species of the octave, or scales. In medieval theory, the authentic Dorian mode could include the note B♭ "by licence", in addition to B♮. The same scalar pattern, but starting a fourth or fifth below the mode final D, and extending a fifth above (or a sixth, terminating on B♭), was numbered as mode 2 in the medieval system. This was the plagal mode corresponding to the authentic Dorian, and was called the Hypodorian mode. In the untransposed form on D, in both the authentic and plagal forms the note C is often raised to C♯ to form a leading tone, and the variable sixth step is in general B♮ in ascending lines and B♭ in descent.

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