The next component of scale theory is the distinction of each degree of a scale or chord. Just as in the above examples, beginning on the 5th degree or 6th degree affects the perfect fifth and Relative Minor respectively – so will beginning on any degree of a scale invoke a mode (the displaced starting point of a scale). For instance, if you were to take a D Major scale (D, E, F#, G, A, B, C#) and displace the starting point from the root, D, to the 4th degree (without changing the intervals), you would begin and end on a G.
Here’s an easy illustration of a mode. Imagine standing on a baseball diamond at home plate. Now, take the C Major scale and place the root C note at home plate. If you were to run the bases, you would start and end at home plate. But, if you started at first base and ran all the bases ending at first base, you’ve still gone around the entire infield, but only changed where you started and stopped. That’s what a mode is, starting and ending on a note other than the root.
Since there are seven degrees in a scale, there is a corresponding mode for each one (excepting the 1st degree or Ionian). Each of these modes provides an array of possibilities in composition of rhythms, chords, and solos.
Ionian & Dorian Modes
The first mode is known as the Ionian, which begins on the first degree. The second mode, starting on the 2nd degree is called the Dorian mode and is commonly found in jazz (as is most every mode) and jazz-rock. This mode sounds much like a natural minor, with the 6 th degree raised.
The Phrygian mode is affected by beginning on the 3rd degree and is insinuative of flamenco and alternative rock. It is also found throughout blues and blues-rock, in 3rd chord dyads (a two-note chord consisting of the root and 3rd).
The Lydian mode, found on the 4th degree, sounds much like a major scale. This mode is prevalent in jazz soloing and again in blues, blues-rock, and rock (likewise, in dyad chords – where the root is coupled with the 4th degree).
The Mixolydian mode is invoked by starting at the 5th degree and sounds like a major scale. This mode will be encountered heavily in every type of rock, blues, jazz, folk, and just about any genre one could possibly name. The reason is, that when coupled with the root, this forms the ever-popular “power chord”.
The mode affected by the 6th degree, the Aeolian, invokes the relative minor of the root (Fig 17). The fundamental distinction between the major (also known as the Ionian) and the minor is the tonal quality. This mode is not as common as the preceding 5th degree but can be found in a few different genres – such as jazz, which of course, employs this mode as does rock.
The last mode, the Locrian, is the most discordant of all the modes and is not typically found in music as a purposely placed effect, but more so as an unintentional phenomenon. Though it is used in jazz to solo over half-diminished minor chords, it does not serve an express purpose or invoke a harmonization like that of the other modes and is mostly happenstance.