A mode is an alternative musical scale that can be derived from the familiar major scale by starting on a different scale tone and which thus has a unique set of characteristic melodic behaviors.
Modes were inspired by the theory of ancient Greek music, and the concept has been a part of Western music since the Middle Ages. The seven modes are Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian and Locrian. Some of these are major, some are minor, and some are ambiguous. There are differences in the psychological effect, with some producing a sadder or holier impression than others.
By far the most frequently used mode today is Ionian, which is the natural major scale and has the interval pattern of two whole tones, a half tone, three whole tones, and one half tone (W-W-H-W-W-W-H). The other familiar mode is Aeolian, which is the natural minor scale and can be derived by starting the Ionian (major) scale on the sixth scale tone. It is common to use multiple modes in both classical and popular music, particularly in the more complex works.