1. Flattened Third (♭3): The major scale's third degree is lowered by one semitone, resulting in a "blue note." This flattened third creates a melancholic and soulful sound when played against the major scale.
2. Flattened Seventh (♭7): The seventh degree of the major scale is lowered by one semitone, producing another "blue note." The flattened seventh adds tension and emotional expressiveness to the music.
3. Use of Diminished Chords: Blues musicians frequently incorporate diminished chords, particularly the seventh diminished chord (dim7), to enhance the tonality. Dim7 chords create a sense of instability and urgency, contributing to the emotional depth of blues music.
4. Chromatic Approach: Blues musicians often use chromatic approach tones to resolve to certain scale degrees. For instance, they might chromatically approach a major third from below (♭3) or resolve a flattened seventh (♭7) to the root note. These chromatic movements heighten the emotive quality of the music.
5. Borrowed Chords: Blues musicians sometimes incorporate chords borrowed from other scales, such as the minor pentatonic scale or the Dorian mode, to add complexity and emotional variation. These borrowed chords introduce new harmonic colors that enrich the tonality.
These alterations of the major scale, combined with the expressive playing techniques employed by blues musicians, such as bending notes, vibrato, and call-and-response vocal patterns, create the distinct and evocative sound of blue tonality.