Gregorian modes

The modes in which Gregorian chants were sung, the most common of which is dorian. A mode is a scale that includes all the pitches of the major scale but does not start on the tonic of that scale. For example, in the key of C, the mode starting on the key of D, consisting of d, e, f, g, a, b, c, d' would be dorian. The mode starting on E would be phrygian, the mode of F, lydian, the mode of G, mixolydian, the mode of A, aeolian, the mode of B, locrian or hyperaeolian, and the mode of C (exactly the major scale), ionian.