There were seven “Greek” modes and in no particular order;
We now use the following, (they have also been referred to as the “Church Modes”)
Ionian is the name assigned by Heinrich Glarean in 1547. Ionia was one of the four ancient Greek tribes.
Dorian is the original Greek name. Dorian was one of the four ancient Greek tribes.
Phrygian is the original Greek name. Phrygian is named after the ancient kingdom of Phrygia in Anatolia
Lydian is the original Greek name. Lydian is named after the ancient kingdom of Lydia in Anatolia.
Mixolydian is the original Greek name. (Mixo-) is a reference to the half-Lydian mode in ancient Greek music.
Aeolian is the name assigned by Heinrich Glarean in 1547. Aeolian was one of the four ancient Greek tribes.
Locrian got its name sometime after the 18th century. (?) Locrian is named after the ancient Greek regions of Locris.
One of the first things I realized in our descriptions of the Dulcimore’s Diatonic scales was the scales starting with Ionian. Yes the Ionian scale is where the modes start, but the Dulcimore starts with Mixolydian off the nut so;
Aeolian first staple
Locrian second staple
Ionian third staple
Dorian fourth staple
Phrygian fifth staple
Lydian sixth staple
Of these seven Diatonic modes we play primarily four. Mixolydian, Aeolian, Ionian and Dorian; Mixolydian and Ionian being the two major modes and Aeolian and Dorian being the two minor modes.
Any of these modes can be played on one string provided the staples are placed in a Diatonic sequence. That is; wide, wide, narrow, wide, wide, wide, narrow. Each mode has five whole notes and two half notes. These are the white piano keys, there are no Pentatonic notes!
To play Diatonic, we add a lower tonic and a perfect fifth accompanying drone. We can refer to the tones by number. The base string lower tonic being (1), the perfect fifth being (5) and the melody note being the upper tonic (8). We must retune to get the placement of the melody string to adhere to the mode, which is to start on the staple we want the mode to start. Once again,
Mixolydian is off the nut so;
Mixolydian open (1-5-8)
Aeolian first staple (1-5-7)
Locrian second staple (1-5-6)
Ionian third staple (1-5-5)
Dorian fourth staple (1-5-4)
Phrygian fifth staple (1-5-3)
Lydian sixth staple (1-5-2)
These are the straight Diatonic modes. We tune to these to play 1-5-8 on the staple starting our given mode. We play a lower tonic, a perfect fifth (dominant), and an upper tonic. This (1-5-8) is our note of final resolution and is where the scale starts.
What you may have noticed missing is any reference to “keys”. There are no keys in Diatonics. Yes, keys may be assigned to any given mode, but that is folks using Chromatics and music theory to describe how they understand the system. Diatonics by definition is absent “any” Chromatic influence, once you inject Chromatics you are no longer Diatonic. One mustn’t learn music theory in order to then learn Diatonics.