Modes
were used to organize the melodic and harmonic elements of
music in the Middle Ages and Renaissance periods. You can
think of modes as scales which use the white keys of the piano.
The Ionian mode (same as the major scale) uses the white keys
from C to C. The six remaining modes also use the white keys
but start on different notes. For example the Dorian mode
uses the white keys from D to D.
During the 17th to the late 19th Century, the modes were not
commonly used, being replaced by the major and minor scales.
Modes are often heard in music today.